Non-illuminated signs with total surface area not exceeding three times the street frontage of the zoning lot (in feet), but in no event more than 150 feet for interior or through lots or 150 feet on each frontage for corner lots, are permitted. Illuminated non-flashing signs with total surface area not exceeding three times the street frontage of the zoning lot (in feet), but in no event more than 50 feet for interior or through lots or 50 feet on each frontage for corner lots, are permitted. No permitted sign shall extend above curb level at a height greater than 25 feet.