One wall sign for each permitted use provided that the area of the wall sign shall not exceed 1 1/2% of the gross floor area of the use, nor exceed 50 square feet in area, whichever is less and further provided that the length of said sign does not exceed 60% of the width of the front facade of the use. In computing permitted sign area, only one face of a building may be used as the principal face. In the case of a use located on the ground floor of a multi story building, only the first floor facade area shall be used for the purposes of calculating the permissible sign area. In the case of a multi-occupancy structure, the allowable sign area shall be distributed among occupants having street level frontage. Single tenant structures shall use the first floor facade area for the purposes of calculating the permissible sign area.