Curse is giving away keys you can redeem to get an in-game t-shirt with the Curse logo on.
Instructions
1. Get your code: Secret World Curse T-Shirt - Digital Giveaways - Curse
2. Go to http://register.thesecretworld.com
3. Log-in to your Funcom account
4. Claim your In-Game Curse T-Shirt!
I did this and I haven't even bought the game yet. So if you are unsure wether to buy it or not, you can just register a TSW account and redeem the key before you purchase the game.