Jennifer Slegg noticed on one of her older sites that Google is showing a notification directly in the mobile search results for the site that the site is not mobile friendly. The message Google shows in the snippet is "your page is not mobile-friendly." I believe it hyperlinks to this Google help page.
Here is what Jennifer sees for her old AdSense site:
When I look at it, since I am not the site owner, I don't see that notification. Instead, I just do not see the mobile friendly label.
I am not sure how new this is, but this is the first I've heard about this.
Forum discussion at Google+.