Check your email:
I got a targeted offer for a free $5 McDonalds GC from MCR. You need to click through the email and enter any code. I used 'roo' and it let me redeem for the arch card.
It it titled:
Get a tasty treat with a $5 McDonald’s® Arch Card®
GREAT REWARDS ARE WAITING FOR YOU Claim your $5 McDonald’s® Arch Card® to get started For good times and great rewards, My Coke Rewards can’t be beat! Earn points from 15 brands and redeem them for gift cards, books and magazines, Coke merchandise and much more—even chances to win amazing prizes. Get started today! Just enter one code to get a $5 McDonald’s® Arch Card®. It’s perfect for a tasty snack, and it’s just the beginning.
(I did get the redemption email too, so it is legit.)