RE: proper ID
I think it started out as a way to identify an airplane in case of a flyaway. Nowadays it's probably more for insurance reasons and to appease the FAA (kinda like the tail numbers on any full-scale aircraft). I don't know about where you live, but I got mine cut at a local sign shop out of vinyl, it only cost like $15 to setup 2 airplanes with my name, AMA, and NSRCA numbers, and they look pretty good, too.