Different layers of information
Seen in Verona, Italy last week-end. Different layers of information, some official (regular signage), some more informal (badly written with Tipp-Ex, to state that drugs can be find on the right).
Another way to communicate that information is to use shoes hung onto a telephone wire as seen on the picture taken in San Francisco few years ago (but this is not more a sort of urban legend):
Anyway, this is part of an ecosystem of signs in contemporary cities that are more less perceived or understood by city-dwellers.