Besides locking a bike up properly, are there other deterrents against theft (such as engraving) that make a bicycle less attractive to a potential bike thief?
It was stolen. :-(
In addition to locking your bike securely with a good lock, there are several strategies you can use:
Where you lock up can be nearly as important as how well you're locked up. If you're in a public, well-lit area, a thief might think twice about stealing a bike. A rack in an isolated, dark area may look more attractive to steal -- there aren't as many potential witnesses.
While some may not have a choice in this matter, if you know you'll have to lock up in a sketchy neighborhood fairly often, you might consider getting a cheap, used mountain bike if possible. Save the flashy carbon expensive-looking bike for club rides and longer road rides.
Take the bike with you
There may be situations where you don't have to lock the bike up. Many supermarkets and big box stores will let you take the bike with you, if the aisles are roomy. Take care to stay out of the way of other customers. If asked to take the bike outside, you can either comply with the request or take your business elsewhere, but be nice about it either way.
Folding bikes are great for this, especially when you can fit the bike into a shopping cart.
Uglify your bike
I've heard it said that you just need to lock up your bike better than the next bike in the rack. That may or may not be true, but consider making your bike uglier than the bike next to it. A terrible rattle-can paint job (i.e., spray painted) will make a nice bike look like a jalopy of a ride.
You can also approximate this by putting a plastic grocery bag over the saddle, using ugly/old bar tape, fenders that are scratched up, and so on.
Wheels and saddles with quick-release hardware are a target for thieves. Much of this can be combatted by locking them up properly (feed a cable through the saddle rails or the spokes of the wheels), but consider replacing these with hardware that needs a tool to open. Maintenance will take longer, but locking up (and unlocking) will be quicker.
The largest deterrent to theft is to make sure your bike is in your line of sight. There are a large number of registries which cater to the idea of a permanent and visible mark on the frame that is registered with an independent 3rd party, such as a police department.
The real issue with those is that so few bikes actually get registered that most police departments don't bother to check for barcodes or RFID tags.
Engraving your name on the frame in a visible spot might help, actually, but there's no way to guarantee that anyone will ever look at it, or contact you if they do recover your bike. I like to include info that is usable for contact, but easy to maintain for a long period of time. A free, web-based email address engraved on the bottom bracket works.
But really, don't leave the bike alone...
Adequate Locks I won't discuss the matter in detail since it's not part of the question, but adequate locks and locking technique are the most important method of prevention for most people. Both the Montreal study and the COPS program support them as the primary line of defense. Also, some seemingly secure locks and locking techniques are so easy to break that they'll attract thieves, so do your research.
GPS Trackers Besides being an effective tool for recovery, if designed properly these devices seem to deter theft, particularly when police in the area are using them to catch thieves. I haven't found official studies or statistics on their effectiveness as a theft deterrent, but one interviewed thief reported avoiding bikes that seem to have a GPS tracker inside, but taking off GPS trackers that were weakly attached to the frame. I also remember seeing a report of a University that deployed several GPS-enabled bait bikes to catch thieves only to have them never stolen. Note that in both circumstances the real deterrent was the possibility of the bike being tracked by the police, not just the possibility of the owner finding the thief.
What you lock your bike to Often people "fly-park" a bike somewhere other than a bike rack without thinking about how secure the structure is. This is dangerous because not only may the structure be easy to dismantle, break, or take the bike off of, but the structure may also not be as safely located as a bike rack. Additionally, fly-parking makes it more difficult to lock a bike up properly (securing both the frame and the wheels with little room for leverage or adjustment). For example, locking a bike to a street sign won't work if the thief can lift the bike and lock up over the sign. Both the COPS report and the Montreal study indicate that a high number of stolen bicycles, as much as 50%, had been fly-parked, and an anti-fly-parking campaign at the University of Minnesota had dramatic success.
Stop stalking Bikes that look expensive are more likely to attract planned attacks. Bike thieves may be contracted to steal a bike a buyer wants or has seen, or may case a bike and come back for it later with powerful tools. Don't park your bike where it's the most expensive bike on the rack, don't park it in the same place every day if you can. If your tire goes mysteriously flat on a bike rack, take it home. Parking a bike overnight or in a risky area greatly increases the odds of this kind of theft happening. Some people uglify their bike to prevent this kind of theft. However, uglifying your bike isn't as effective against other kinds of theft. Petty thieves who are just looking for a quick $100 don't care as much if your bike is rusty and duck taped.
Prevent stolen parts This is often overlooked, but a quarter of cyclists in the Montreal study were victims of bicycle parts being stolen--usually wheels or seats, but sometimes other accessories. Either use a cable lock to secure these, deter theft by removing quick-releases and other DIY techniques, or invest in locking nuts, bolts, and skewers (Pitlock, Pinhead, and Zefal are some of the sellers for these).
Take it inside If you had a Ferrari, would you leave it overnight in a good garage or a NYC street? That's why many cyclists prefer indoor storage, despite the hassle. If theft is a serious concern where you live, consider investing in a folding bike.
What kind of works:
Bicycle Registration This is recommended almost universally, and both the COPS paper and the Montreal study showed that it improves chances of recovering a stolen bicycle. However, the Montreal study showed that cyclists who registered their bicycles were far more likely to have been victims of bicycle theft (and after theft bicyclists are likely not to register their new bike). This is hypothesized to be due mostly to the difference in demographics and attitudes in the groups, but it goes to show that bicycle registration should not be depended on to prevent theft.
Where and when you lock your bike Identifying a risky situation helps you take preventative measures you wouldn't have otherwise taken, like storing a bike indoors. Montreal study confirmed the obvious fact that the shadier and more urban the area, the more likely it is to be stolen. However, the study noted that most people overestimate how safe their own neighborhood is. The study also confirmed that nights are the most frequent time for theft, although afternoons was a close second. Summer also is a peak time for bike thefts.
Video Surveillance sounds like a great idea, as who would want to be filmed stealing a bike? Too bad that according to the Department of Justice it isn't a "suitable deterrent," unless there's someone responsible for securing the premises like a security guard. So don't leave your bike in a dangerous CCTV area overnight, trusting that the cameras will scare away thieves.
Inexpensive bikes Many cyclists use "beater" bikes for commuting and trips to higher risk areas, saving their expensive bikes for recreational use. It's difficult, however, to prove that this is a very effective theft deterrent. The Montreal paper points out that cheap bikes are among the most common thefts, even if they're old. This is after accounting for the large popularity of these bikes and types of locks used. This correlation may, however, have to do with extra things that owners of expensive bikes do to protect their bikes that weren't studied, like where they store their bikes or how expensive their locks are. The study also showed that mid range bikes ($500-1500) are the least likely to be stolen, showing that increased risk of theft of top-end bikes is real.
"Britain's most stolen bikes" reported in these statistics, were midrange bikes, and not necessarily the most popular ones either. These British statistics contradict the other evidence that mid-range bikes are safest, but also confirm that expensive bikes are not the most commonly stolen. In summary, the typical person with a cheap bike is actually more likely to have their bike stolen than the typical person with an expensive bike. So having a cheap bike is not a dependable way of preventing theft (although securing your bike as if it cost a few $1000 may be effective). Using a cheaper bike for higher risk situations does minimize the cost of a theft, which is one reason why the practice is so common.
You can also ride a customised or unusual-looking bicycle. Most bike theives are either looking for transport or something easy to sell. Transport theives you can't do much about, but they usually don't carry decent lock-breaking tools either - a good D lock will stop them.
Theives trying to resell will look at your bike and if it's distinctive and has no easily-sold components, most of them will leave it alone. Why both spending 20 minutes stealing, stripping and selling something that's going to fetch $5? Even theives have standards.
So rather than a beater bike, ride a tall bike, or a folding bike, or a chopper. Or just work up a set of distinctive but functional mods to your preferred bike. Like a 27" front, 700c rear wheel, laced in a funky pattern. Or fit a banana seat.
It seems that having only clipless pedals works too. It's not as easy to ride off with. This is the only thing that's stopped me from switching to my combined pedals.
I have a sit up and beg bike for getting around town and locking up near dodgy places, Its a 31 year old bike its in perfect mechanical working order, dynamo/lights. And it has some perfectly placed rust/corrosion on the stainless steal parts. I never wash it if possible. People seem to look the other way, little do they know its a mean machine in disguise.
Hope I haven't jinxed it....
You can purchase custom nuts and bolts that are tamper proof. If you couple that with two u- locks, it would be nigh impossible to steal the bike.
I live in a high theft area.....and I have 3 bikes...
Thieves want easy, intact bikes. And seriously, you can't always keep the bike in sight.
Finally.... Never use cable locks! Snip. Your bike is gone...
Simply fit a wicker shopping basket on the front! No,I'm not joking; You must try to read Mel Allwood 'THE TOTAL BIKE MAINTENANCE BOOK' pages 28-33.
Cover brand names on your bike with tape.
One of my bikes is a Cannondale.
First thing I did was to cover with tape all the letters.
Looks uglier, but doesn't cry "I'm an expensive brand!".