The vandalism happened Friday around 9 p.m. Oakland police say several car windows were also smashed during an Occupy Oakland march.
"And they started yelling and yelling," Obama 2012 campaign worker Tommy Perry said. "Then they started shooting the paintballs, throwing rocks, and one guy had some little thing and started busting out the window. You can see I got paint all over me and everything."
Some campaign workers think the backlash toward the Obama campaign stems from the recent federal crackdown on medical marijuana dispensaries.
Oakland police followed the marchers but made no arrests. There were no injuries.