A declarant may maintain sales or rental offices, management offices and models in units or on common elements otherwise restricted to residential use only if the declaration so provides and specifies the right of the declarant with regard to the number, size, location and relocation thereof. The use of any such sales or rental offices, management offices and models by the declarant shall be confined to the sale, rental or management of units in the cooperative where such units are located. Any sales or rental office, management office or model not designated a unit by the declaration is a common element, and, if a declarant ceases to have an ownership interest in the association, he ceases to have any rights with regard thereto unless such office or model is removed promptly from the cooperative in accordance with a right to remove reserved in the declaration. Subject to any limitations in the declaration, a declarant may maintain signs in his units and on the common elements advertising the cooperative owned by the declarant for sale or lease.