Every retail dealer in internal combustion engine fuel advertising the price of such engine fuel on any sign shall include in the price shown on such sign all taxes imposed with respect to the manufacture or sale of the motor fuel offered for sale, and every such sign shall either contain a statement of the taxes included in said price, or, without specifying the amount thereof, shall state that such taxes are included in said price. All figures, including fractions, upon said signs, other than figures and fractions used in any price computing mechanism constituting a part of any pump or dispensing device, shall be of the same size.