I like the remote control idea...but how about something different? Say a remote control slice of pizza, or a pizza box, perhaps? Something that would make you look twice if you saw it rolling towards you. :)
Actually, I like the idea of a pizza box, and how someone sees a pizza slice and has to decide whether to pick it up or not. But then again, most people won't eat random food running around in public.
Maybe it's something that is elusive. Something that we chase after. It could be a saddam hussein or osama. But those are things that are too seriously politically charged. Maybe it's something more symbolic. Something that we chase after in life...
It could be a dollar bill attached to the car. But would someone really take it off? It would have to say something like, "this dollar bill is FREE, if you can catch it!"