Development signs. Signs advertising the sale or development of the premises upon which they are erected, when erected in connection with the development of the premises by a builder, contractor, developer, or other persons interested in such sale or development may be erected and maintained, provided:
(a) The size of any sign is not in excess of 10 square feet; and
(b) Not more than one sign is placed upon any property, unless such property fronts upon more than one street, in which event one such sign may be erected on each frontage;
(c) Any such sign shall be removed by the developer within 30 days of the final sale of the property.