That's the Shoulder Sleeve Insignia (SSI) of the 30th Infantry Division, active from 1917–18, 1940–45, and 1947–74 in the National Guards of North Carolina, South Carolina, Georgia, and Tennessee. The "OH" shape of the insignia stands for the nickname of Andrew Jackson, "Old Hickory"; the "XXX" for 30. The insignia was sometimes mistakenly worn sideways (horizontally) during World War I.