I have 2 Colt carry handles in front of me and neither has the square mark near the sight.
Of these, one has "A-7" on the left, while the other has "AH" at the same place.
Just looked at the other stash of about a dozen, maybe 20. Several have the square, others do no, and one has what looks to be "0°5." where the square would be.
IOW, all over the place and all were supplied by Colt and came off new M4A1s.