Standards to measure and compute the amount of sign area permitted in the various districts are herein established as follows:
(a) The total area of all signs permitted on a lot in accordance with regulations set forth in the following sections shall include:
(1) The area of the faces visible from a public way of all signs, except that only one side of double-sided pole or ground signs shall be counted, plus,
(2) The area of signs placed upon the surface of windows or doors, plus,
(3) The area within a rectangle enclosing the lettering, modeling or insignia of signs integral with a wall and other signs not designated as a panel.
(b) The frontage of a building shall be the number of lineal feet of the facade facing the principal street or containing the main entrance.
(c) The frontage of a lot shall be the number of lineal feet that the lot abuts on the principal street.