[ricki]

Streamers, wrist bands, tags and stickers have been used in various parts of the world. I would choose something that is easily visible, unique, non-divisible and readily breaks away if tangled by a powered up kite.

People can be pretty strange about this sort of thing given that they exist solely as a rule to allow them to continue to ride. Guys have counterfeited stuff, cut streamers in two to share with friends, etc.. I wouldn't get too obsessed about making it totally inviolate but would consider some past problems along the way toward putting together what you will.

Important point, I second the sentiments about doing something. It is easy to have things die in committee with the problem still remaining. So, figure out the minimum needed, what seems to be fair and reasonable and do it.

Good luck