In a pinch, and no duct tape available, then you could always go into the men's restroom at a local highway gas station, and get several colored condoms------they should be able to stretch to roughly 10". Now a days they come in crazy colors which would make very noticeable numbers.
But as far as making them stick on the car you are on your own-----I know a way they could stick, and you could have fun doing it---but even I won't go there.
Trying to get faster