This lovely engraved hard hat of unknown origin is up for sale on eBay. It's decorated with images of offshore oil drilling work:
Hello, up for auction is a vintage/antique B.F. McDonald engraved/hand hammered hard hat. Fantastic oil drilling themed hat. The hat has off-shore oil rigs all around the sides and a helicopter towards the top/front and a helicopter landing pad around the back. The metal work is stunning. Signed "Wisna" on the top center (5th photo down). The interior straps are plastic, with vinyl on the front where it touches the forehead. Hat is stamped "McDonald - T - Cap Standard - Mine Safety Appliances CO." on the interior bill (10th photo down). It looks as though someones name used to be on the front, as many of these hats do, and it got incorporated into the design - see second photo below.
Link -via Boing Boing