Bike Register site, which the Police themselves will use if your ride is ever stolen and then recovered.
Then a code is marked on your cycle in an unnoticable position to aid identification alongside the frame number and description. (In the image I've smudged my number, it is a lot clearer than the image suggests!) Thirdly, an optional sticker is supplied, as a deterrent to potential thieves.
I don't know how permanent the coding is (remember you've still got the frame number logged) but apparently it eventually dries so clear that it is likely to be overlooked by a thief.
Seems like a no-brainer, now. Maybe this bike has a fighting chance of being wornout instead of being nicked. Apparently this process makes your cycle 57.5% less attractive to the scum that take our much-prized rides.
If you want to catch up with these guys in London, check your local papers - or even better, make sure you visit the Cycle Show at Earls Court from the 8th to the 10th of October where the Marking Crew will be there all day long.
Outside London you'll have to check with your local Police Force - and if they're not running a scheme like this, complain until they do.