Signs locating and advertising subdivisions of land and projects requiring site plan approval, which have received tentative or final approval by the Borough, provided that each such sign shall not exceed 24 square feet in area, shall not exceed two in number and shall not be located closer than 20 feet to any street line. Such sign permits shall be valid for a period of six months and then such signs shall be removed, unless the permit is renewed. Such signs shall be removed, in the case of land subdivisions, when either 75% of the lots created have been built upon or after 75% of the lots have been sold by the developer, whichever should occur first, and in the case of projects receiving site plan approval, upon the issuance of a certificate of occupancy.