I was recently playing MW2 on PS3 and noticed that some of the players have the word "Unbound" where their clan tag should be on their player card.
What exactly does this mean? Are they playing on a modded PS3? Does this also occur on Xbox 360?
It looks like it's a hack of sorts accomplished by editing your save file. A set of instructions to accomplish it can be found here. There were other results in Google as well searching for "unbound clan tag". All in all, it doesn't do anything for them other than changing their clan tag.
I do not know if something similar would be possible on the 360.
You get this in an "Infection" lobby, and yes this does occur on XBox 360. (I have unbound on my playercard)