The 03 a3 (Which I hope you know is a 1903 a3 rifle) has a sight on the reciever the 1903 sight is on the barrel. The barrel band, bayonet lug assembly are milled, the rear of the receiver is clean, and the front handguard ends in front of the rear sight.
The trigger guard on the 03 is a nice looking piece of milled steel. On the 03A3 the trigger guard is stamped and spot-welded; ugly, in other words.
Hope this helps to determine which one you have.