GBuy, the online payment system that will be launched by Google on June 28, will enable online merchants to become "trusted GBuy merchants", so they will have these kind of badges on their websites.
Google ads will most likely be CPA ads and will have a "Google Certified Merchant" text that will try to increase people's trust in using the system.
Using this system, Google will find more information about what people actually buy and will update its ad ranking system.
Screenshots from Aneil Webber.
Note: these screenshots are not from Google, so the final product may look different.
Update: Here are some leaked screenshots from Google.
More about GBuy:
GBuy to launch this month
Make payments with Google
Playing with privilege
1 hour ago