reading left to right would be the primary headquarters - Army (Arabic numeral with "A"), Corps (Roman numeral) or Division (Arabic numeral with no suffic for Infantry Divisions, follwed by the "delta" for armored divisions, or with "AB" or "ABN" for airborne divisions, next comes the regiment or battalion (followed by "-I" for Infantry, the "delta" for tank, "FA" for field arillery, etc. On the right side of the vehicle would be the company and indivisual vehicle number.
Your M4A1 is assigned to the US VII Corps, the 741st Tank Battalion. This is one of the two battalions that landed on DDay with two companies of Duplex Drive M4A1s and one reinforced company with standard tanks fitted for deep wading. The 741st was the battalion that had their two Duplex Drive companies almost wiped out for being launched too far out in heavy seas. Many of the deep-waders made it ashore and fought well, taking heavy casualties. The unit was refitted and served through the rest of the war in Europe - commonly with the US 2nd Infantry Division.
Gary B.