Off-premises advertising signs, billboards, portable signs, roof signs, pennants, ribbons, streamers, spinners or similar moving, fluttering or revolving devices are prohibited in any zoning district unless approved by the Town Board, on a case-by-case basis, after a public hearing thereon. These prohibitions do not apply to decorative displays. Flashing, oscillating and revolving signs are prohibited in any zoning district unless necessary for public safety or welfare.