It looks like Google is testing a new design for the Google Guaranteed badge or icon. The previous design was a green circle with a white check mark inside of it. The new design is more in Google colors, it is a shield with a checkmark in it, using Google colored lines.
Tom Waddington posted a screen shot of the new design on Twitter:
Here is what it looks for me right now:
I do prefer the new design versus the old one, it matches better.
Forum discussion at Twitter.