I looked at a Colt 6920 yesterday and have a question about the markings on the upper.
On the right side close to the rear sight, it was marked with a big “C”. The “C” was stamped, not raised. Farther forward, it had a keyhole looking symbol that was raised.
I’ve seen this keyhole symbol on cheaper uppers at the gunshows before.
Is this an actual “Colt” upper or is someone trying to pass this off as a Colt?
I think there was actually a thread about this posted somewhere on the website a few days ago. I have a Colt 6920 with these same markings and while I can’t seem to recall what they mean I can assure you that my Colt is not a knock-off. Wait… it just came to me. It’s the marking for Cardinal Forgings. They forge a lot of AR uppers: http://www.dekalbforge.com/cardinal/index.htm
The keyhole is the forgers mark. Colt does not operate its own forgery. There are actually only a few forgers who supply the entire AR market.
Colt buys the raw forgings, and then machines them in house. So you have the C mark denoting Colt, and the keyhole mark denoting where the raw forging came from. Alcoa and Cardinal are two of the big forgers, and they also make tons of other forged products. Its the only way to make AL forgings cost effective.
Colt switched to the “engraved” C not too long ago. However they do make parts in batches, and then keep them around until that supply is exhausted. You might buy a recent production Colt but look at the barrel, and it was made several years ago. 6920’s and the more popular models will be made more often…but something like a 6721 not so much.
dont worry, I have the same exact markings on my Colt 
Cerro forge = keyhole
Cardinal forge = stylized forge marking. check out an LMT for the forge mark. or do a search on this site. i’m sure there are pix somewhere on here.