For those of you that want to commute on a nice bike in bad neighborhoods, let me give you a few tricks that have served me well.

1. Replace all quick release fixtures with tooled fixtures. This is generally a small investment.
2. Take a black marker to all component markings, making all those Deore XT's look at first glance like no-name-brand cheapo components.
3. Either give your bike a crappy paint job -- spray paint some garish, noticeable color. Dont' bother making it beautiful, but make sure any bran markings or indication of quality of bike dissapear. An easy alternative here is wrap the frame in packing tape, which will make your bike look like a beater, but preserve the original finish if you ever want to resell it.
4. Use a good lock, but it should look old and beat up, not like you take your bike too seriously.

In my experience, which is sadly rather high, bike thieves tend to look for shiny, and easy targets of opportunity. Camoflouging your bike as a beater will cause most to simply scan right over it.

Incidentally, the following happned to my roomate in Paris, with a brand new $3K mountain bike: He pulled up to a fixture of some sort, leaned his bike against the fixter, and started fishing around in his bag for a lock. Whilst doing so, a theif road up on a beater bike, sprung off said beater, sprung on roomates fancy pride and joy, and road off while my roomate looked on in shock and horror.

Probably wouldn't have happened if his bike looked like a beater.

A further point is looking for a good locking place -- somewhere with nice bikes on parade, in view of gendarmarie, or in view of many cyclists (where a thief might suppose you are amonge said cyclists) are good choices, as is underneath a security camera, such as those typically found in car parks. Finally, workplaces often have a sheltered area where you can lock your bike in relative safety.

Last or not least, you can leave the QR on your bike seat, and take it with you when you are leaving the bike for an extended time. This tends to be quite discouraging as it both makes your bike look like an abandoned beater, and makes riding off on your bike uncomfortable.

For those of you that want to commute on a nice bike in bad neighborhoods, let me give you a few tricks that have served me well.

1. Replace all quick release fixtures with tooled fixtures. This is generally a small investment.
2. Take a black marker to all component markings, making all those Deore XT's look at first glance like no-name-brand cheapo components.
3. Either give your bike a crappy paint job -- spray paint some garish, noticeable color. Dont' bother making it beautiful, but make sure any brand markings or indication of quality of bike disappear. An easy alternative here is to wrap the frame in packing tape, which will make your bike look like a beater, but preserve the original finish if you ever want to resell it.
4. Use a good lock, but it should look old and beat up, not like you take your bike too seriously.

In my experience, which is sadly rather high, bike thieves tend to look for shiny, and easy targets of opportunity. Camouflaging your bike as a beater will cause most to simply scan right over it.

Incidentally, the following happened to my roommate in Paris, with a brand new $3K mountain bike: He pulled up to a fixture of some sort, leaned his bike against the fixture, and started fishing around in his bag for a lock. Whilst doing so, a thief road up on a beater bike, sprung off said beater, sprung on roommates fancy pride and joy, and road off while my roommate looked on in shock and horror.

Probably wouldn't have happened if his bike looked like a beater.

A further tip is to look for a good locking place -- somewhere with nice bikes on parade, in view of gendarmarie, or in view of many cyclists (where a thief might suppose you are among said cyclists) are good choices, as is underneath a security camera, such as those typically found in car parks. Finally, workplaces often have a sheltered area where you can lock your bike in relative safety.

Last but not least, you can leave the QR for your bike seat, and take the seat with you when you are leaving the bike for an extended time. This tends to be quite discouraging as it both makes your bike look like an abandoned beater, and makes riding off on your bike uncomfortable.