§ 1229. Sign required on privately-owned vehicle used in delivery of mail. 1. Every person operating a privately-owned vehicle in delivering the United States mail to the addressee thereof shall affix to such vehicle a white sign, visible from the rear, containing the following statement: U. S. MAIL Such statement shall be in black lettering at least four inches in height. 2. Every person who violates the provisions of this section shall be punishable by a fine not exceeding twenty-five dollars or by imprisonment for not more than ten days or by both such fine and imprisonment.