It shall be unlawful and shall constitute a misdemeanor offense for any person to destroy, tear down, shoot at, deface or erase any printed matter or signs placed or posted by or under the authority of this chapter: Provided, however, That this section shall not apply to the owner, his agents, tenants or lessees, of the lands on which such signs or printed matter are posted. Each such sign so destroyed, torn down, shot at, defaced or erased shall be considered a separate offense under this section.