It’s called Google “+1” and it’s used to mark the results (pages) that you appreciate after a search. Once the result is marked, your preference will be saved and shared with other users.
This new addition comes shortly after Google introduced the option to block unwanted sites and is only available to internet users who have a Gmail account and are logged. Currently, the “a+1 is in the experimental stage.
To try this Google feature, go to google.com/experimental and subscribe to your experiment. In addition to the “+1” feature, there are other facilities that can be tested: Keyboard shortcuts and Accessible View.