(a) Any sign or device stating or relating to the minimum octane rating or to the retail price of motor fuel, or designed and calculated to cause the public to believe that they state or relate to the minimum octane rating, or to the retail price of motor fuel, posted or displayed on or about premises where motor fuel is sold at retail, or on public property adjacent thereto, and in view of any public highway, road or street, shall clearly and legibly state in figures the minimum octane and, in figures and fractions of uniform size and prominence, the price per gallon and, separately stated, the per gallon amount of tax to be collected in connection with the sale.
(b) Nothing contained in this section shall be deemed to prohibit any separate sign or decal posted or displayed on or about premises where motor fuel is sold at retail, relating to premiums, trading stamps, or other promotional devices, or the per gallon amount of tax imposed upon the sale of motor fuel, provided any sign pertaining to price of merchandise other than motor fuel, clearly and legibly states in letters the same size as the figures and fractions stating such price, the name or designations of such merchandise.