In a stairway leading down to the subway platform of the N/Q Canal St. stop, a pair of doors face each other on a landing. About every three days for more than a year, I've seen graffiti painted on both doors. Each time, the day after the graffiti appears, so does a fresh coat of cream-colored paint. By my count, those doors are covered in at least 100 coats of paint and must be more than an inch thicker than they were last year.
Update: Probably looks something like this if you cut it open. (thx, emmet) Or this.
