‘Keep Holland Clean’ is the tagline for this ad campaign applied to the rear end of buses in Amsterdam. The crusade is not to keep garbage off the streets, but to keep it out of the city buses.
Apparently some people that use this form of public transportation are being lazy; they are not using the proper waste bins and are leaving trash on the buses instead.
It seems pretty effective, if it were realistic. I can almost see people tossing their used coffee cups at the back of the bus, only to have them bounce off and land in the street!