Look at the poster again. Looks like a photoshop job too me. The text looks too clear and uniform and unaffect by the ripples in the poster.
I don't reckon this poster even exists or has been stuck anywhere. It's someone's attempt at starting some sh*t, and everyone is biting, IMO.
EDIT - Haha... ok, I guess it probably does exist. Just read about it. But if all this proves just one thing.... its that Photoshop is the true evil, it makes you doubt everything!!! Its worse than the Matrix!!