Signs containing street number designations, household nameplates, postal boxes, historical markers, and directional signs shall be permitted in all zoning districts, provided that they do not exceed two square feet in area. Advisory signs such as those with text similar to but not limited to "private property, "no soliciting," "no trespassing," "no hunting," "beware of dog," shall be permitted in all zones provided that they do not exceed two square feet in area and that advisory signs with the same or related message shall be separated by a minimum distance of 50' in order to prevent the adverse impact of sign clutter on adjacent properties.