Images from the protest:

http://www.flickr.com/photos/32033721@N00/7637636396/

See also:

Obama cheered, jeered in Oakland
Carla Marinucci and Joe Garofoli
Updated 08:55 a.m., Tuesday, July 24, 2012
A few blocks away from Obama's Fox event, hundreds of protesters gathered throughout the day at the city's medical cannabis center - Oaksterdam University - to protest the federal crackdown on medical marijuana. They marched and held signs reading "fight crime not cannabis" and "Obama keep your promise." Antiwar activists and other liberal protesters dissatisfied with Obama's policies joined the demonstrations.
http://www.sfgate.com/politics/article/Obama-cheered-jeered-in-Oakland-3729481.php