GMC Trucks porcelain sign is a must-have for any collector of automobile advertising especially gas and oil memorabilia. It features the recognizable GMC lettering on a 11 3/4-inch 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. GMC Trucks & Automobiles. 11 3/4 inches in diameter. Bright colors w/ porcelain on both sides.