Google Featured the Annotations to its +1 button, which shows the friend who had already +1d with an hover over it. It will show the faces of the friends.This feature is already there in the Facebook like button.
With this improvement Google is making it +1 button more social and better.
“You may have already noticed faces and names when you hover over a +1 button,” Google Developer Advocate Timothy Jordan said in a post on the Google+ Platform preview. “This change rolled out late last week. Now, you can make these recommendations even more visible to your users. Simply update the +1 button code, and an inline annotation will show next to the button.”