On residential, commercial or industrial buildings having rear entrances which open upon an alley (street not included) or private driveway, the numbers assigned for the front or principal entrance may, in addition, be required on the rear entrance, garage or gate, at the discretion of the building official. (Ord. 6038 § 2, 2006; Ord. 5998 § 2, 2006; Ord. 2856 § 2, 1974; 1957 code § 2.15.070.)