Spooge5150,
Your hammer marked CE II is a Colt piece, the circled M is probably a subcontractor as I've seen variations of M marked components before.
In going over my notes, I've come up with the following list of markings found on hammers by manufacturer and serial number range, as used on orignal production M16's. It is NOT inclusive but can be used as a guide in identifying the origin of surplus hammers.
Early Colt M16A1 (800,XXX), 2 on Left side
Colt M16A1 (4,000,XXX), 1,2,3 or 4 within a C on left side transitioning with = or - by 4,500,XXX.
H&R M16A1 (2, 057,XXX), 1,2,3 or 4 within a circle on left side. H&R produced M16A1's will be found with Colt manufactured bolts (MPC) and carriers (C) marked components.
GM/Hydramatic M16A1 (3,000,XXX) 1,2,3,or 4 within C, indicating Colt supplied FCG parts to GM. GM M16A1's also used Colt manufactured bolts (MPC) during production, although bolt carriers were unmarked.
Colt M16A2 (6,XXX,XXX), marked on left side with CE I, CE II (C indicating Colt, EI indicating revision I, etc). followed by E I, E II, followed by E 3 over N or E4 over N (N possibly being a subcontractor).
FN M16A2 (7,XXX,XXX), marked on left side with E3 over F or E4 over F.
EMCO rebuilt M16A2's and conversions. E3 over E, E4 over E, E over M, and E left side w/ M on right side. The last two were probably made for EMCO by a subcontractor being "M".
I haven't made notes on new production M4's or A4's as of yet. As far as parts marked with only a subcontractors mark as in M, unless they are observed as original components of new production weapons they should be considered as replacement parts.
One final note that may be of help. A SOUM (Safety Of Use Message) was published in Febuary of 1990 calling for the replacement of all M16A2 hammers that were marked with an "H" on the left side, as they were defective. This was due to an out of spec disconnector hook that allowed the weapon to double or fire full automatic when placed on Burst. So in the unlikely event you come across one, don't buy it.
Hope this is somewhat helpfull,
Wpns Man