Any advertising sign, billboard, commercial advertising structure, or statuary, which is lawfully existing and maintained at the time this chapter became effective, which does not conform with the provisions hereof, shall not be structurally altered and all such nonconforming advertising signs, billboards, commercial advertising structures and statuary, and their supporting members shall be completely removed from the premises not later than three (3) years from the effective date hereof. (Prior code § 16-42)