This is part of an international 190-city protest against the Iraq War (with 70 of the cities are in states that voted for Bush in 2004). They've been organizing on MySpace, and distributing flyers in schools that say "if you like Bush, stay in school Oct. 5."
After the market from Justin Herman Plaza to the Civic Center and back, the activists plan on camping out at the Embarcadero Center for the evening, listening to speakers, and (this is our favorite part) locking a 40-foot effigy of Bush in a mock jail, for "war crimes." Guys, go all the way! Make it a Bush piñata! Bush Ter Down!