Further to Clutch's thread, I want to post up a bike watch system. I've been thinking about this for a while now, and the idea may have been triggered by another member on this board. If so, I apologize for stealing your idea.
Basically, we get small, discrete decals made up onto which we write/type/print our user name and place these in a non-obvious location on our bike. All of us would put the sticker in the same place. The location should be hard to spot casually, but easy to see if you know where to look.
Then, when you see a bike you can take a subtle look for the decal. If nothing is there, carry on. If there is a decal, then when you see the rider you ask if he is on bcsb. If he says no, call the fuzz. If he says yes, ask his user name. If he gives you a name that doesn't match the decal, call the fuzz.
OK, let 'er rip. Shoot some holes in the idea. I can take it.
(BTW, I'm sure most bikes are stolen and parted out pretty quick, but on the off chance that some doofus takes his ripped off ride for a boot, we might have a chance to catch him).