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.