Update: This offer is expired.
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2,500 Bonus Starwood Points Promo Link 
Via the link above, you can get get 2,500 bonus Starpoints for adding an authorized user on your SPG credit card account. You can add yourself, a family member or whomever you choose, as long as they are at least 15 years of age.
A social security number is required for adding the additional user. There is no hard credit pull for the additional user, though the new account will show up on their credit report.
Limit of 1 bonus per account.
is the limit per SPG account or Amex account?
Per SPG account.