In M2-1 Districts, only non-illuminated signs and signs with indirect illumination are permitted. The surface area of all signs on a zoning lot shall be limited to:

(a)        one sign displayed from the wall of a building limited to 1.5 square feet of surface area for each linear foot of street wall or 150 square feet, whichever is less, and further provided that such signs shall not exceed a height of eight feet, and shall not extend to a height greater than 20 feet above curb level ; and

(b)        one sign not affixed to a building limited to one square foot of surface area for each 200 square feet of street wall or 30 square feet, whichever is less, and further provided that such signs shall not exceed a height of five feet above curb level.