Markings would be mirrored front and rear. The triangle (Δ) is used to denote armor units and can be used after the division number as well as before the regimental number. Although for the most part, regiments are non-entities in the US Army with a few exceptions.
For example there were the 1Δ, 2Δ, 3Δ for 1st, 2nd and 3rd Armor Divisions in the US Army and the 49Δ and 50Δ for the 49th and 50th Armor Divisions in the Army National Guard.
But when used for battalions within a regiment, the triangle comes between the battalion number and regiment number.
For instance, I served with the 5th Battalion, 77th Armor Regiment. While there were other numbered battalions (1st thru 6th), the 77th Armor Regiment did not exist as a stand alone entity with a regimental headquarters. Back in WW2, when regiments did exist, there would be a regimental headquarters and three battalions. Company A, B, C would be 1st Bn, D, E, F was 2nd Bn, G, H, I was 3rd Bn, etc.
Battalion bumper numbers would be 1Δ77, 2Δ77, 3Δ77, etc. or sometimes could be seen as 4-77Δ, 5-77Δ, 6-77Δ depending on how that particular unit decided to paint them on.