displaying a copy of this poster, together with New York Times bags and a trash can, on a tree in my parking strip does seem to be paying modest dividends:

 

• bags are vanishing fast enough that I have to beg friends to save their NY Times wrappers
• occasional bags of poop appear in the trash can
• the endless offerings of abandoned dog-poop on my (corner lot) parking strips do seem to be diminishing.

Origin: this Post Globe article.