In all districts, temporary signs, including signs advertising land or premises available for purchase, development or occupancy, or announcements of special events, or signs of mechanics or artisans, shall be permitted, provided that:
A. Real estate signs shall not exceed six square feet in area. Not more than two such signs shall be erected for any property held in single or separate ownership. Such signs must be removed by the person or persons erecting them upon completion of the sale or rental of the property.
B. Other such signs shall not exceed 18 square feet in area, shall be limited to one per property and shall be removed immediately upon the completion of work. The site or building upon which the sign was erected shall be restored to its original condition upon removal of such signs.