GM Diesel Power porcelain sign is a must-have for any collector of automobile advertising especially gas and oil memorabilia. It features the recognizable GM lettering on an 8″ by 5″ porcelain surface. Whether you are displaying this sign as part of your collection in your man cave, shop, bar, or garage, or giving it as a gift, you can also browse my other auctions for more vintage gas, oil, aviation, automobile, motorcycle, and hunting signs. GM Trucks & Automobiles. Bright colors w/ porcelain on both sides.