Here is an "easy" answer, make a reflector with a simple RFID tag embedded in it. Make them look like all the reflectors you normally have on your bike. Create a repository for registering reflectors and give a free reader to every bike shop that wants to combat bike theft.
Will determined thieves swap all the reflectors? Sure. Does it raise the 'cost' of stealing a bike? Yes.
Alternative idea, put the tag in the bike seat. You can re-use pet tags, you can then re-use pet tag injectors and pet tag readers.
This is a good idea, actually. Just taking email addresses for an idea might well still be sketchy but that's as may be. Someone should do this even if that someone doesn't my email in the meantime.