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 building, contractor, developer or other person interested in such sale or development, may be erected and maintained, provided:
(1) The size of any sign is not in excess of 20 square feet.
(2) Not more than two signs are placed upon any property in single and separate ownership unless such property fronts upon more than one street, in which event two such signs may be erected on each frontage.