The code is "RETURN".
The brochure says, "When you tell friends about your Discovery Cove experience, they'll want to try it for themselves - and when you give them this card, they can save $50 on their own visit.* (Offer expires December 17, 2006. Restrictions apply.) Be sure to mention that this exclusive offer for past guests and their friends features new all-inclusive meals, snacks and beverages throughout the day, as well as a consecutive seven-day, unlimited-use pass to either SeaWorld Orlando or Busch Gardens Tampa Bay. Book your visit to Discovery Cove Now. Visit DiscoveryCove.com or call 1-877-4-DISCOVERY or 1-407-370-1280 and use promo code RETURN."
Hope this helps. Try the code first, and if that doesn't work and you need the card, feel free to PM me.