First Amendment (aka 1amsf.com). They guide your group in hands-on workshops introducing the city’s graffiti and street art culture. Your teams then design their “art” and message, and after an introduction to stenciling and a little spray can control practice, “do their thing” on an (authorized) exterior wall or on take away canvases… or on t-shirts, totes… or whatever you think you can get away with.
Workshops can be at their gallery or they can come to you, or can include walking tours of some of the best SF street art. They seem like really cool and genuine people, so… do that. :)