Number. For each parcel, one temporary real estate sign may be displayed on each parcel of land or part thereof that is for sale, lease, or rent; however, when more than one dwelling unit or nonresidential space on a parcel of land is for sale, lease, or rent, there may be one real estate sign for each such unit or space. For a parcel with dual street frontage, such parcels may have one additional temporary real estate sign per frontage.