In addition to the underlying district sign regulations, the following regulations shall apply to all signs:

(a)        signs may not occupy more than 25 percent of the total area of the storefront measured from curb level to 10 feet above curb level;

(b)        all permitted signs which project from the front building wall shall be located not less than 10 feet above curb level; and

(c)        signs may not cover columns, cornices or sills.