One sign per parcel of real estate advertising the sale, lease or rental of the premises upon which the sign is located shall be permitted, provided: the sign shall not exceed six square feet in sign area and four feet in height above the adjacent ground level within the RLD, R-1-30, R-1-20, SCR-1, AR-1, AR-2 and RR-3 Zoning Districts; shall not exceed 24 square feet in sign area and eight feet in height above the adjacent ground level within the I, LI and CC Zoning Districts; and provided the sign shall not exceed 16 square feet in sign area and seven feet in height above the adjacent ground in all other zoning districts. Should the parcel of real estate advertised have no common boundary with a public road, an additional such sign may also be located upon the parcel providing access from the public ways. Should the parcel of real estate advertised have a boundary in common with two public roads, then two such signs shall be permitted, one adjacent to each such road.