There is no link or coupon code, it will be displayed when you log in online under Account Activity tab, may be targetted.Here is the fine print:
Offer Valid Through 12/31/12. Discover must be used for payment.
You will be awarded an account credit on one purchase of $150 or
more from 12/01/12 to 12/31/12 up to a total credit of $15 during
this period. Allow up to 8 weeks after the promotional period for
this credit to be added to your account. Purchases made using
Near Field Communication (NFC), virtual wallets, or similar
technology may not be eligible.
Discover Card Coupons