Section 28-501.5. Construction

This chapter shall not be construed to grant
  the right to place or maintain a sign on any building or premises  where
  the  placement or maintenance of such sign would otherwise be prohibited
  pursuant to the zoning resolution, the administrative code or any  other
  provision  of law. No permit for a sign issued hereunder shall be deemed
  to constitute permission or authorization to maintain a  sign  which  is
  unlawful  pursuant  to  any other provisions of law nor shall any permit
  issued hereunder constitute a defense in an action  or  proceeding  with
  respect to such an unlawful sign.