Signs may be illuminated by either:

(a)        internal illumination; or

(b)        an external source that shall be so arranged that it projects no more than 12 inches from the sign it illuminates, and so that no direct rays of light are projected into adjoining buildings or the street. No flashing signs are permitted nor are flashing or rotating light sources except illuminated signs that indicate the time, temperature, weather or other similar information, pursuant to the definition of flashing sign in Section 12-10.