Metropolitan Cartography's description on their Flickr photostream, this blunt warning was posted here here in Brooklyn, on Montrose Ave between Graham Ave and Humboldt St. I actually found these photos separately in a Google search while researching the text "IF I CATCH YOU PUTTING THE DOG HERE TO TAKE A SHIT I WIll CAll THE COPS", from the first photo, but I'm assuming both signs authored by the same vigilante.
It looks like the white sign above was probably an attempt to improve the brown sign on the left with a dash of color. However, poor planning with overly liberal letter kerning on "SHIT I" resulted in a bad case of the Squeeze with "WIlLCAllTHE". Some things that make this sign special are the unnecessarily dotted uppercase i's, and an extremely rare sequence of uppercase and lowercase L's in the same word. This combination has only happened once before in the history of lowercase L's.
I took a virtual walk on Google Maps Street View to see if I could find the sign, but no luck. Let me know if you see it in real life, maybe interview the SUPER 250F?