WWII USA 13th armored regiment - 1st Armored Division
During WWII, there was little if any standardization of unit markings of the armored divisions in the US Army. In certain divisions, there were general practices that were followed aside from the bumper codes. The US 1st Armored Division used slanted bars indicated each of the battalions. A circle positioned near the bar indicated the 1st Armored Regiment while the 13th Armored Regiment used a square.