Allen,
He is listed in Tennesseans in the Civil War as "A. C. Sgt. F & S.", not A .C. S.
Since Gay Mathis in his earlier post noted that he was an Ensign, my initial suggestion that Frank Moses was the Regimental Color Sergeant, would be validated. And, of course, the sketch in Lindsay's Annals note that he was "the gallant standard bearer of the Sixty-third," at Drewery Bluffs, reinforces.
Ensign also being an archaic term for standard bearer.
I think what we need to determine is what the prefix 'A' in "A. C. Sergeant" stands for.
George