American Express is offering a 50% bonus when you transfer Membership Rewards points to SPG to targeted Platinum Card holders. The usual transfer rate is 1,000 MR Points to 333 SPG Points, and with this bonus you can essentially transfer Membership Rewards points to SPG in a 2:1 ratio (1000 to 500).
This offer appears to be targeted, even among Platinum card holders. I have the American Express Platinum card, but was not targeted for this offer. It looks like some members received an email, but you should also be able to tell by logging into your Membership Rewards account.
I don’t really think this is a super deal, but might be useful to some. For example, if you need to top up an uncommon frequent flyer award program that can only be transferred from SPG. However, keep in mind that you have transfer a minimum of 1,000 Membership Rewards points.
Since SPG has merged with Marriott, you can also use this method to indirectly transfer points from Membership Rewards to Marriott. With this promotion, you will basically be transferring Amex to Marriott at a 2:3 ratio. That is actually better than Chase’s Ultimate Rewards transfer rate. As a result, if you value Chase UR and Amex MR points the same, this could be particularly useful.
The offers is valid from October 17, 2017 to November 17, 2016 (11:59 pm CT).
(HT subintima1 on Reddit)