A billboard, signboard, or advertising sign shall not be permitted as an accessory use, except that the placing of an illuminated "For Sale" or "For Rent" sign not more than eight (8) square feet in area may be permitted as an accessory use, and except that churches and other institutions may display signs showing names, activities and services therein provided, and that during construction of a building one (1) non-illuminated sign showing the names of contractors or architects for such buildings shall be permitted, providing such sign shall not be more than eight (8) feet square in area, and shall not be set more than five (5) feet in front of the established or customary building line, and such sign shall be removed immediately upon completion of the building.