(DEAD, Only Available to New Customers. Sign up Here and get $50 Bonus) You probably already know about the Double Rewards on the Discover It card for 12 Months. There is no sign up link. Originally you had to call but now you can also do it through the online chat at Discover.com.
The second option would probably be the best way to go, since you can save a copy of the chat conversation as confirmation. Discover doesn’t send you en email or a letter after you sign up, and nothing shows on your account regarding this offer.