Earning a Modern Warfare Clan Tag isn't as difficult as it seems. It's not actually related to your performance in-game, and can be done quickly.
With Call of Duty: Modern Warfare Season 2, you can now play in a clan, or Regiment, with your friends. You can set a custom Clan Tag for your regiment, and you can make it gold to show off your team.
Modern Warfare Clan Tag: How to get a Gold Colored Clan Tag
First, you need to have a Regiment and create a clan tag for it in the Social menu.
You then set the Regiment's clan tag as your own by going into Barracks and then Identity. You can select a Clan Tag and make it match your Regiment's.
When you set that, if you hover over Clan Tag option, you'll see a prompt on the bottom left to press a button (dependent on your platform) to Switch Clan Tag. Doing this will make it gold. Now you can represent your clan and still have some bling. Every 12 year olds dream.