There can't be anything more ignorable than the posters in the New York City subway stations. That is, when they are put up properly and doing their job. However, things can start becoming interesting when they're ripped off to put up new ones. It exposes a whole history of putting up and ripping up posters, which can sometimes yield some interesting abstract results.
I stumbled upon this by accident. If you frame the picture just right, you can capture something abstract. It was just interesting to me how an act of destruction could yield such interesting images. I took some time out and stopped at every local stop on the M train from Rockefeller Center to the 71st Continental Avenue stop.
These are some of the most interesting ones I saw.