A sign or signs referring to or advertising the premises upon which it is located or displayed, or to the identity of the occupant thereof, or to a service rendered thereon or therein, or to a product or item available therein, or to a permitted trade, business or profession carried on thereon or therein. One such sign may be erected on any entrance wall and one on any wall facing on a street, and one on any wall facing an off-street parking area, and one on any wall facing a railroad track, and such signs shall be erected parallel to the face of such wall, not extending more than 12 inches therefrom, the bottom of which shall be at least seven feet above the level of the sidewalk, and shall be rigidly and securely attached thereto. The area of each sign shall not exceed two square feet for each foot of wall width; the maximum height of such sign shall not exceed two feet and the maximum width shall not exceed 90% of the width of the storefront or wall of that portion of the premises occupied by the occupant erecting the sign and upon which it is attached. In determining maximum width, the maximum width of the storefront or main entrance wall of the premises or the width of the wall upon which any such sign shall be erected, whichever is less, shall govern. Where there shall be more than one occupant of any building, the total areas of all signs of all occupants, taken in the aggregate, shall not exceed the maximum requirements above set forth for each wall upon which any sign is permitted to be erected.