Last month I wrote about Google Testing the Mobile Friendly Icon, which wasn’t the first time they tested it, this month Google officially rolled-out a label that tells users whether or not a site is Mobile-friendly. During their testing, they also tried doing an icon that tells users that a site is NOT mobile friendly, which I also wrote about recently. Here is an example of the label that Google rolled-out to tell users that a certain page is Mobile-friendly.
Google also rolled-out a new testing tool for developers and users to test a site to see if it is Mobile-friendly.
Here is an example of a random site testing using the Google Mobile Testing Tool.
So there you have it, Google said that they are still testing the tool and hoping to add more to it in the future. But for now, get your site mobile-friendly because it will also be a ranking factor.