Before you paint it, take a picture of it and report it to the police. They keep records of grafitti, and many of the taggers use the same "tag" over and over. When they do get caught, the cops will pile on as many cases as they can.
I used to work at a store at 39th and Powell, got a new tag at least once a week. I never let them have the satisfaction of seeing it or showing it off to their buddies, I just painted over it as soon as I saw it.