Every person who sells tobacco products at retail shall post conspicuously and keep so posted at the place of business a sign, no smaller than ninety-three and one-half (93½) square inches, to ensure that it is likely to be read at each point of sale, stating the following:  STATE LAW STRICTLY PROHIBITS THE SALE 
  OF TOBACCO PRODUCTS OR SMOKING PARAPHERNALIA 
  TO PERSONS UNDER THE AGE OF EIGHTEEN (18) YEARS 
  PROOF OF AGE MAY BE REQUIRED