You can receive 2,500 bonus Starpoints after you add an additional person to your Starwood Preferred Guest Credit Card from American Express. The offer was sent out by email, but I don’t see one in my inbox. However it should work, even if you didn’t receive the targeted e-mail. Log in here. The offer is for the personal card, but not the business version.
The offer for 2,500 Starpoints expires on September 19, 2016. Card Members are limited to one-time receipt of 2,500 Starpoints through this email offer. Bonus points will appear on your Starwood Preferred Guest statement 8-12 weeks after you add an additional Card.
Keep in mind that Amex requires a SSN for AUs, so it will show on credit report. You can even add yourself as an authorized user. DoC points out that authorized user accounts do count towards the Chase 5/24 rule so keep that in mind.