I've done a few similar to that for various friends' race cars (as well as on my own, in the photo below) though mine say "OBJECTS IN MIRROR ARE LOSERS."
I did all the graphics on a friend's Tyrrell F1 car and I put one of those on his mirror without telling him. He said he never noticed for the longest time until midway through a race one day and it surprised him so he almost ran off the track from laughing.
