One bulletin board sign, not exceeding 12 square feet in surface display area shall be permitted for a house of worship, school or permitted institutional use provided that if the bulletin board sign is not attached to the facade of the building, it shall be located no closer than 10 feet to a street line. Such signs may be illuminated by backlighting or by direct lighting provided the latter is so screened that light is not directed or reflected toward any adjacent property. Any lighting must be white or yellow.