This particular sign is at the entrance to one of the neighbourhood schools, so the chance is great that the culprit attends this particular school. Can the vandalism be simply ascribed to boredom? Is the act perhaps intended to impress friends, or a potential girlfriend?
It's easy for adults to shake their heads in disapproving dismay at the destructiveness of "our youth", but I guess on reflection one might rather be dismayed at the destructiveness of people - after all, some vandalise road signs, others vandalise countries. Which is the greater evil?