Actually, I've been waiting to see a thread about this. I was just too lazy to start one by myself xP

Here's what happened to our clan:

I'm the leader of a lvl 38 clan on MW3. Our clantag is 'UoSR'. I've checked out the BO2 clan unlocks and they say that golden clan tags are supposed to be unlocked on lvl 10, just like on MW3. So I thought in the meantime I'll just put in 'UoSR' without colour, like anyone else could do. It certainly didn't have any special colour. But after I played several matches it suddenly turned into gold by itself. No hacking/modding! Worked the same way for my clan members. The funny thing is: Once it turned itself into gold, you can change it again to whatever you like and it stays golden oO However, it may be that in this case it'll just change back after some matches. Didn't try that, don't want/need to.

So why is that? My guess is that they made it so that you have to have reached clan lvl 10 on either MW3 OR BO2, and golden clan tags will unlock for you on both games, no matter on which one you achieved lvl 10. That actually makes sense as the clan itself is the same for both games and the golden clan tags ('UoSR' in our case) are reserved for that specific clan anyways. Would be nice to hear some official confirming this, tho.

To anyone reaching Level 10 on BO2, entitled to their Gold Clan Tags.

Using the PC is easier to explain what to do. Sign into Elite, Click Clan HQ, Choose option 'Manage Clan' (Only for the Clan Leader), On the first page it gives you your clan name, motto and band (for MW3) and to the right, a clan tag box. Type in your ideal clan tag and wait and see if it's available. If it is not, you may need to vary it a little using capitals and lowercase letters.

Let me know how it goes.