Google is calling out webistes with "faulty redirects" in mobile search results to save users from having to deal with the "common annoyance" of tapping a search result only to be redirected to a site's mobile homepage.
This occurs when a site isn't properly set up to handle requests from smartphones. As Google notes, it happens so frequently there are actually comics about it. They point to this one from xkcd:
Google is simply noting in the search results that the result "may open the site's homepage," and provides a link to "try anyway."
To avoid this happening to your site, Google recommends first searching on your own phone to see how your site behaves, and then checking Webmaster Tools to see if Google has sent you a message about detecting any of your pages redirecting smartphone users to the homepage. Luckily, Google is kind enough to show you actual faulty redirects it finds in the Smartphone Crawl Errors section.
After that, Google says to investigate the faulty redirects an fix them by setting up your server so it redirects smartphone users to the equivalent URL on your smartphone site, and if the page on your site doesn't have such an equivalent, to keep users on the desktop page, rather than sending them to the smartphone site's page.
"Doing nothing is better than doing something wrong in this case," says Google Webmaster Trends analyst Mariya Moeva.
She notes that you can also try using responsive design. Google's full guidelines for building smartphone-optimized websites can be found here. Google also has a help center article specifically on faulty redirects here, which you might find useful.
The new disclaimer feature is only appearing in English search results in the U.S. for now.