Believe what you want about the Tenderloin, and its surrounding neighborhoods, but know that this neighborhood is one of the most affordable parts of San Francisco. And it has many protected buildings that house all sorts of interesting people. Murals are on the walls now, but it was mostly graffiti, stencils, and posters up until galleries and organizations went large on the walls.
The Tenderloin - Civic Center Stencil Archive is updated, and includes new images. Just so you all know, this archive also keeps images from Union Square, Polk Street, Van Ness Ave., and Mid-Market. I have walked through the TL many times (and gave tours through it for about five years), and though grim and sad at times, I have found stencils and interesting walls to look at.