Temporary construction trailers and one sign not exceeding 50 square feet, advertising the prime contractor, subcontractors, architect, financing institution and similar data for the period of construction beginning with the issuance of a building permit and concluding with the issuance of a certificate of occupancy or one year, whichever is less, provided such trailers and sign are on the site where construction is taking place and set back at least 15 feet from street and lot lines.