Harmon Carbon does sound pretty sweet but it is actually Harmon/Kardon (EU speaker manufacturing company among other things). As for your question, I believe both models shows as a 831c but only the HK has the Champagne(Gold) front trim on it.
Where did you get the phone? If it came out of the original box it should've been accompanied by a pair of Harmon Kardon black and gold earbud headphones and the box, obviously, states that it is the HK version as well.
I'm assuming you didn't get it new from the store so it would be somewhat difficult to check which one it is by looking in settings...easiest for sure way to know is to reboot to bootloader ( with the phone OFF hold down the volume down key+power). The second line from the top of the screen should say "CID = SPCS_001" or "CID = SPCS_004."
SPCS_004 = HK
SPCS_001 = Non-HK standard edition
It also MAY say "11111111" instead which is called SuperCID and is a modification someone would've had to have done to the phone before you got it...in that case it is most likely the standard edition but we'll have to check elsewhere to be sure so let us know^^