I believe it is more of a cruisers thing?
It's more of an old time hard core biker thing. We brothers have been giving each other things to put on our bikes since returning from WWII. It's a way to carry your brother with you in your travels down the road, have good luck and the all important warm fuzzies. It could be a piece of leather, a beer can tab, a foot peg or other piece for your bike and even a bell. Mainsteam RUB as it may seem, it means alot to old and new riders alike. We do sort of the same thing here on the Org. The Pay it Forward thread is full of peeps giving others parts and things, mostly for free. Superstition? maybe. But knowing some one cared enough to give you something is priceless.