AC Spark Plug Service porcelain sign is a true gem for any collector of automotive, oil & gas memorabilia. Measuring 12 and featuring a classic red color scheme, this porcelain gas sign is a true must have item. Whether you are displaying 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 gas, oil, aviation, automobile, motorcycle, and hunting signs. Vintage Automotive porcelain sign. AC Spark Plug graphic. Excellent gloss w/ porcelain on both sides.