In San Francisco, property owners are required to paint over graffiti on their buildings. I've had to do this myself on a couple occasions. (If you don't repaint, the city will come do it and fine you.)
Anyway, I noticed this last night as we walked down Eighth Street (near Howard). It seems pretty obvious that the graffiti predates the box. The question is: Was it more work to draw the box and write the message — considering the time it took to find the correct spelling of "graffiti" — than just painting over the graffiti?
If you can't make it out, it says, "Painting within the above box is expressly permitted and shall not be considered 'graffiti' according to article #23 of the SF municipal code."