Temporary construction trailers and one temporary sign not exceeding 32 square feet, advertising the prime contractor, subcontractor(s), architect, financing institution and similar data for the period of construction beginning with the issuance of a construction permit and concluding with the issuance of a certificate of occupancy or one year, whichever is less, provided that said trailer(s) and sign are on the site where the construction is taking place, are not on any existing proposed street or easement and are set back at least 30 feet from all street and lot lines. There shall be at least one working telephone in the trailer.