hard to find late 1930's vintage american industrial lightly embossed stamped steel "shut down this machine" oil refinery cautionary sign likely fabricated by the national safety council for the standard oil company of indiana. the sign contains bold white lettering against a baked black enameled background. the desirable halting hand logo containing the "safety first" slogan is prominently displayed in the top left corner. contains four nail or screw holes for mounting purposes. measures 11 x 8 1/2 inches.