It is unlawful for any person in the city of Pinole to write, stamp, affix, mark, or attach any inscription, name, picture or other thing upon any building or a part thereof or upon any fence, tree or other property owned or controlled by the city of Pinole or in any manner injure the same; provided, that this section shall not apply to the acts of persons duly authorized to perform such work thereon. (Prior code § 51).