Google is constantly testing new PLA formats, and the newest is for “top” and “best” product queries.
On Mobile, the ads look a little bit different, with blue ribbons instead of the grey circle boxes:
Before you go optimization trigger happy and start adding in “top” and “best” keywords to your products, make sure you read this:
According to Google Adwords’s Official Twitter account, “when a user searches for “best” queries we display products ordered based on user ratings. Once the top rated products are selected, the rank is determined by the same factors as a regular PLA auction.”