The total surface area (in square feet) of illuminated signs on a zoning lot shall not exceed two times the street frontage of the zoning lot (in feet), and in no event shall exceed 50 square feet for interior or through lots or 50 square feet on each frontage for corner lots. The vertical dimension on any illuminated sign shall not exceed 2 feet, 6 inches, nor shall illuminated signs project more than 10 inches from the surface to which they are affixed.