I would find those responsible and punch them

I would find out who did it. I would insure that the perpetrator's parents had to pay to have it removed and repaired.

Unless... How well do you know your kid?

Still wet? I would take a photo of it [in case I decide to go to the police] and then try to find something to smooth it out so the words disappeared. And then I would try to find out who might have done it.