It's not known when the campaign sign was put up in the Railroad Avenue location, but the Danville Weekly learned of it early Friday afternoon.
Contra Costa County Clerk Steve Weir, whose office is overseeing the May 5 mail-in election, said that there are few local rules dictating when and where campaign signs can be placed.
"The state and localities have tried to regulate the placement of election signs but they invariably lose on Freedom of Speech," he explained.
Weir said the basic rule of thumb is that the sign should not visually impede the public nor should they be on traffic signals or crossarms. He said that in the case of the post office, because it is a federal building, it would be up to them to police it.
"I would guess that the federal government has strict rules about electioneering," he said.
Postal officials confirmed that having such campaign signage inside the branch is illegal. Post office sales associate Mark Willis, on being informed of the bumper sticker in the lobby, immediately took it down.
"This isn't allowed inside the post office," Willis said. "We can't put up advertisements of any kind. We can't even put up something for Primo's Run."