Rene Turrek, a German graffiti artist, painted a BMW with large images of the Hulk. Then he covered those images with a special type of paint that becomes temporarily transparent when in contact with hot water. It's like those Hot Wheels toy cars that change color when immersed in water.
Don't make him wet. You wouldn't like him when he's wet.
-via Superhero Feed
https://en.wikipedia.org/wiki/Ranma_½