I have a barrel with this marking on the top, forward of the FSB:

(C)       MP

5.56 NATO 1/7

My question is this; Is anyone familiar with the (C) mark... that is a "C" with parenthesis around it?
I am aware that a "C" by itself indicates a Colt barrel, but I have not seen one with the ( ) around it.
I was told this was in fact a Colt barrel when I acquired it. This may not be unusual, but I can't remember seeing it before.
...then again...I don't get out much  
-Vic

Not personally acquainted w/the ( ) marking, but I'm wondering if it's not meant to designate something different about the barrel, from the standard issue GI specs.

Like:
Is it a government profile, or a heavy (behaind the front sight base) type?

Is it fully chrome lined, or is it unlined, or just chamber lined?

Colt has been known to vary markings on civie market stuff from what they put on the things that are for, or duplicate, GI spec pieces.

C MP 5.56 NATO 1/7  
Colt Magnafluxed, in 5.56 NATO, 1 in 7 twist

Thanks for the replies ...I'm thinking that shamayim may have hit on it. This could very well be a "chrome chamber" designation. That is what the barrel seems to have upon visual inspection.
It is M4 configuration, light under the handguards.

-Vic