Graffiti censorship

When I first lived in Japan ten years or so ago, I don't recall seeing much in the way of graffiti - neither the "artistic" sort, nor the scrawled tags which are presumably the tagger-equivalent of what dogs do to lampposts. It's particularly prevalent around Harajuku, and not even the post boxes are safe - although Japan Post doesn't take graffiti lightly and is applying the ultimate sanction, censorship.