Signs may be illuminated; however, the actual sources of illumination shall be shielded from public view. Illuminated signs may be lit during hours of operation or until 10:00 p.m., whichever is later. Neon tubing as a medium for signs is prohibited in all zones except for Commercial, General Business and Shopping Center Zones where indoor neon tubing signs which are visible from the exterior of the building may be placed indoors in the front facade window(s) only to a maximum size of 1% of the front facade, but not to exceed 36 inches by 36 inches. Flashing signs are prohibited.