The agency of a licensee who holds an exclusive listing, shall be respected. The licensee shall cooperate with other brokers on property listed by the licensee exclusively whenever it is in the interest of the client, and share commissions on a previously agreed basis. Negotiations concerning property listed exclusively with one broker shall be carried on solely with the listing broker. Signs giving notice of property for sale, rent, lease, or exchange may not be placed on any property without the owner's prior consent.