Such sign or signs as may be deemed necessary by the chief engineer or the assistant chief engineer of the board shall be erected, at the cost and expense of the permittee, on the access area, and the same shall be approved as to design, number, location, erection and construction by said chief engineer or the assistant chief engineer; at least one of said signs shall have placed thereon notice to all persons of the nonliability of the State, the district or the board for damages to person or property by reason of any use of the permit or the exercise of any privilege thereunder; no other sign or signs shall be erected or placed on the access area.