Bumper Markings

I've been lightly sanding the various spots looking for original markings. So far it looks like (thankfully) no serious prep work was done for the numerous paint jobs my M715 has received. So far I have found the original hood & tailgate markers: U S ARMY 03E74768, I've uncovered the National Symbols on the doors. And now I've recovered the numbers on the bumperettes which is what I have a question about. I know the left is the Major Comand, Intermediate Comand & Unit and the right is the Order of March but I cant make sense of mine. They are: left 5 AES and the right is ATC 556. Does anyone have a clue on these???