One detached sign, per entrance, separate from any building or structure, for the purposes of identifying the premises or directing traffic into the premises, shall be permitted so long as the sign does not exceed 40 square feet in area and so long as no portion thereof, including any foundation, base, or frame therefor, shall be closer than 10 feet to any property line at street intersections. The sign shall have the written approval of the chief of police and building inspector stating that such sign creates no traffic hazard. Such approval is to be on permit forms supplied by the community and economic development department of the city.