FYI, here are the markings on my Army issue M4.
Barrel- C MP 5.56 NATO 1/7 (marked on top of barrel infront of front sight)
Front Sight Base- B99 RI(in a small circle), located on right side of sight base
Upper Receiver- C AF, numbered rail, T2-T12 rear to front, marked M4 in front of carry handle
of U.S. GOVT.
CAL. 5.56 M.M.
COLT'S MFG, CO. INC.
SAFE, SEMI, BURST, on both sides of the receiver
Buttstock- No Markings
Carry Handle- AA on left side near rear sight
Bolt Carrier- C on left side
Bolt- MPYC, the Y is underlined
Thought you guys might be interested.
Edited to show additional carry handle markings.