Target used to sell this little strip (mabe 6"s long and 3/32" wide) of neon stuff that was used inside your car (the package showed it above a radio), I think it plugged into a ciggerete lighter outlet.
I'm sure you could modify some of them to work on your car.
Personally I think neons are kinda dumb, but thats just my opinion (maybe its just because all the "potato cannon tailpiped cars in town have them) so dont go flaming