I discovered only three or four slabs with clearly defined pigeon feet in all of Lower Manhattan. Conditions have to be just right for an imprint like this to occur, as the cement cannot be too wet nor too dry. And, of course, you need one well-placed pigeon. I once observed residents from an East Village tenement carefully guarding their freshly-laid sidewalk from an impending etched obscenity. Yet, it would be far more difficult to stop a pigeon from making his or her defiant mark.