I've seen a lot of nerdy graffiti in big cities like Amsterdam, Berlin, Paris etc. Everything from Mario to something relatively obscure like Monkey Island.
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I'm fine with street art as long as it's not anything hateful or on actual historically important buildings (or local businesses/houses/whatever). Some ugly grey old abandoned warehouses/walls or whatever are totally fine. A bit of human creativity can be a beautiful thing. In Berlin specifically street art is historically and culturally very important, given that city's history and modern art status. At this point I'd say it's one of the city's greatest attractions.