Mouser and odd symbols

There's a bodega (NYC-speak for small convenience store) on the corner of 6th Ave. and Watts Street that has a very handsome cat who occasionally walks out and greets me when I walk past. He's the sweetest guy with the disposition of a kitten but the owner just informed me he is 13 years old. Unlike most cats, he never bites or claws after having had enough of stroking. He loves affection and will lie there on the sidewalk as long as you offer it.

As I stood up to leave he looked at me bewildered as if to say "Hey, where are you going?"

Last night while waiting for my friend Tatiana to meet me I noticed this odd symbol drawn into the chipped edge of the building. Very very small. (Reminder: you can click on images to enlarge.)
I glanced at the other side and found a symbol with a V, also very small. I wondered what these symbols meant, who may have put them there and why? So curious.