Banksy Wiki. He's a huge artist in the UK. Anyway, he came to SF and made some art on some walls. His art is meant to send a message about anti-capitalism, anti-war, anti-government. Basically anarchy. Or socialism. Whichever you prefer. Here are some of his murals.
Also, one of my favorite pieces is a Banksy work. I feel that it sends one of the strongest messages I have ever seen in a mural.