Someone somehow managed to write this on my car by cleaning off some of the scudge... I actually have no idea how. They made it *look* like they were just using their finger, but experimentally fingers (and scrubbing by hand, and car washes) don't have any actual effect on the dirt.
They must have used a knife or something? Anyway, it's probably there for the duration since *I* can't get the dirt off by any means I've tried.