At about 2:45 a.m., an overnight employee from the department was performing routine street and sidewalk cleaning duties when he says he spotted two men tagging a wall inside of the tunnel.
The employee promptly reported the act to San Francisco police, the department said.
Officers arrived on the scene and the employee was able to point out the suspects, who were found near Sacramento Street.
Police initially arrested both men, but later released them, after issuing one of them a citation for vandalism, according to the department.
Residents are encouraged to call 9-1-1 when they see an act of vandalism in progress, but are reminded to exercise safety when doing so, police said.
Kristen Peters, Bay City News