Business zone or use. Within this zone, advertising or commercial displays for commercial uses, which are acceptable to the Secretary of the Interior, may not exceed four square feet in area, may not be self-illuminated and may be placed only on the property on which such commercial use occurs. No flashing, blinking or moving signs shall be permitted. Roof signs are prohibited. Facial signs parallel from the structure to which they are attached. Signs projecting at a ninety-degree angle from any structure shall not project more than four feet from the structure to which they are attached nor be placed lower than eight feet above the adjacent grade. No sign shall be so constructed or attached to any building as to obstruct any window, door or other opening of the same. The maximum number of signs permitted per business lot shall be one.