In Germany such stuff is handled by the "Ordnungsamt" (office of public order, roughly translated). They're not policemen so they don't have the authority to arrest, but they can and will issue fines for littering, graffiti, improper advertising and the likes.
At least graffiti and trash keeps the rents down, plus it looks nicer to the eye than the bullshit uber-clean concrete crap that passes for "luxury flats" these days.
This way police is free to handle actual crime.