Video of the woman in action is posted on YouTube.
The video shows the woman jump out of the van, yank the sign out of the ground then take off and head back to the van.
The homeowner set up cameras to catch neighborhood dogs who were using his yard as a bathroom.
On their Web site, the California Republicans urge people to call police and report yard sign thefts.
They also list several other alleged McCain/Palin sign theft locations in Sacramento County, Alameda, San Joaquin, Los Angeles, Madera, Fresno and Tulare.
Signs supporting Proposition 8 are also disappearing from yards, according to the California Republicans.