I was wondering if this was a good derailleur, found a specialized bike on Craigslist with this on it.
That says 8SIS (i.e. 8 speed Shimano Index System), a thing Shimano used to mark some of their derailleurs with when the system was still new-ish.
It's a basic Alivio level part -- nothing special, on the mid to low range. You can replace it with any 7-9 speed Shimano derailleur.