I got an email from AmEx today announcing this. I think all the small businesses are probably in the US so it doesn't really help me, but I thought it might be useful to some of you since that would equate to 6 Marriott points per dollar.
From now until December 31, you can get 2X rewards when you use your enrolled Starwood Preferred Guest® Credit Card from American Express to Shop Small in your neighborhood. And with more places than ever now accepting American Express, there's never been a better time to get out and show your love for small business.
Get 2X rewards by earning 1 additional Starpoint® for each dollar spent
using your enrolled Card at small businesses listed on the Shop Small Map, through 12/31/16, on up to $100,000 in purchases. Terms apply.*