American Express is upgrading its Sync program with Twitter to let cardholders buy stuff by using a hashtag.

Starting Monday, AmEx customers who sync their cards can buy items if they use the right hashtag. The first such item is a $25 AmEx gift card, which will go for $15 if you tweet #BuyAmexGiftCard25. Other offers will be rolled out on Wednesday Feb. 13 at noon EST including an Amazon Kindle Fire HD for $149.99 (a $50 discount), an Xbox Controller for $29.99 (a discount of about $10) and an Xbox 360 4GB console with a three-month Xbox LIVE Subscription and two game tokens for $179.99 (which is the price of the console without those extras.)

If consumers opt for those items and use the correct hashtags, then they will get a verification from @AmexSync, which will contain a confirmation hashtag. Cardholders then have 15 minutes to tweet the confirmation hashtag to confirm their purchase. If they do so, the item will be shipped to their home within two days for free.

The program expands on AmEx's Sync program for Twitter, which rolled out last March. That initiative rewarded participating cardholders with discounts on items if they used various hashtags.

Though the program appears to be breaking new ground, AmEx isn't the first company to see potential in Twitter-based commerce or "t-commerce." In 2012, a startup called Chirpify linked up with PayPal to let users buy and sell things on Twitter using @ handles.

For AmEx, the move may be less about boosting a fledgling ecommerce platform and more about promotion; With each hashtag, users give a tacit endorsement to the program and, by extension, the AmEx brand.

Image courtesy of iStockphoto, Magnez2