[yasuki]

https://www.marriott.com/rewards/promotion.mi?promotion=MS13

いろいろなパターンがあるようですが、私は以下でした。

To earn your free nights:

Register online or call 888-MARRIOTT (627-7468) by March 15, 2013
Stay twice at any participating hotel between February 1 and April 30, 2013
Earn 1 free night after every second paid stay, up to 3 free nights
Enjoy your free nights at any of nearly 3,000 category 1 – 4 hotels.