Indiana is the state to which he is officially accredited; the state from which he entered service. Remainder of the inscription is his rating and unit. Indicates he was a Technician Fourth Grade assigned to 818th Engineer (Aviation) Battalion.
Aviation engineer battalions were elements of the Army Air Forces. Normal duties were building and maintaining air facilities. The battalion isn't credited with participating in the Battle of the Bulge but it's possible he, individually or with a small component of his battalion, was temporarily detailed to a combat-, construction- or general service engineer unit. Not likely but possible.
Another possibility is the inscription is based on information from his discharge papers. If so, the 818th was simply the unit to which he was assigned - the custodian of his records - while he was being processed out of service and may or may not have been the unit he served with overseas.
Technician Fourth Grade - abbreviated T4, T/4, Tec4 or Tech4 - was an enlisted specialist rating entitled to the base pay of a Sergeant, 4th Pay Grade.