Okay, this one makes sense - Times SQUARE.
Maybe this one is a comment on the missing World Trade Center Towers.
I can't for the life of me figure out any meaning behind the seahorse with a missing square.
I'm assuming this last one has to do with a square peg in a round hole?
P.S. I'm not positive the postal service will actually handle these. I think I'll mail one to myself and find out. Stay tuned...