I had a discussion about this in a CJ a few years ago - they were refusing to refuel me without stickers by the overwing caps. Helpfully, they offered to give me a couple. We put them on and started fuelling. When the fueller lifted the nozzle out a dribble of fuel spilt over the nice new sticker. The nice black lettering promptly dissolved and some dribbled into the tank.
oh how we laughed..