In addition to the signs otherwise permitted by this chapter, there may be displayed, on any lot, up to three flags displaying any otherwise legal symbol, message or information, commercial or noncommercial; except that off-site commercial flags shall be restricted as set forth in this chapter. No such flag shall exceed 24 square feet measured by one face of the flag only. Any such flag shall be mounted directly to one flagpole. A "flagpole" is a pole intended and placed solely for the support and display of a flag or flags, and does not include utility poles, light poles, trees or other sign structures. All flagpoles shall be erected vertically, or within 45° of the vertical. No portion of any flagpole shall be sited within 10 feet of a property line. No flagpole shall extend more than 35 feet in height above grade or, if mounted on a building, 55 feet above the average finished grade of the building.