There is artistic graffiti.
There are quite a lot of graffiti also in Japan. 
http://koueninfo4.fc2web.com/rakugaki/photo-2.html
http://www16.tok2.com/home/kouen5th/rakugaki-3/photo-3.html
A lot of artistic graffiti exists in graffiti, too.
Graffiti of the station lavatory etc. have there is not an obscene reaching an extreme though as for graffiti on the outside, there are a lot of considerably healthy one. 
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