In this case, the graffiti here was so remote that it had been in the same place for many months. I took the photos Saturday (as well as more I'm not done sorting through), and one of the pieces is signed 2010. So graffiti hounds aren't spraying the place constantly (or there's enough of the place free that they've got enough other walls to spray).
Anyhow, I really like the "demon" one. To me, the M looks like the face of the demon.