Westin is offering 500 SPG points in exchange for you to make your own bed (or reuse your towels). Another way to phrase it is: “500 SPG points in exchange for saving them costs in labor and laundry.” A third way to put it (as Starwood Corp. would like to tell its customers): “Help the earth and enjoy a gift from us!”
Instead of the 500 SPG points, you can choose to get a $5 gift card to be used at the Westin restaurant, lounge or gift shop. I was recently at a Westin in Pasadena, CA and the Westin in San Francisco, and saw the card with the following message upon arrival:
You tidy, we treat
You may choose to decline housekeeping service for the following day by hanging this card on your door before 2am. In return for going green, we will deliver a $5 gift card that you may use towards any Restaurant, Lounge, or Room Service purchase within the hotel. If you prefer, you may exchange unused gift card at the front desk for 500 SPG points.
The catch here is you will need to put the tag out by the door before 2AM. I guess the Westin staff need to determine which room will not be serviced the following day and issue your card on time. You will not qualify for this offer if you are only staying for one night.