Directional signs indicating the location and direction of premises in the Borough available for or in process of development in the Borough, but not erected upon such premises, and having inscribed thereon the name of the owner, developer, builder or agent may be erected, by permit, and maintained, provided that:
(a) The size of any such sign is not in excess of six square feet and not in excess of four feet in length; and
(b) Not more than one such sign is erected for each development; and
(c) Any such sign shall be removed by developer within three weeks of the final sale of the property.