These notifications are being sent via Google Webmaster Tools and via email. It is also being sent to sites that are simply not mobile friendly at all and typically, the webmasters know their sites are not mobile friendly. What we have here is Google reminding these webmasters their sites are not mobile-friendly and issuing a warning that the pages won’t rank well in mobile search. There are clear signs that a new mobile ranking algorithm is about to launch at Google. Google told us they are experimenting with it since November. They also launched a mobile friendly testing tool, mobile usability reports in Google Webmaster Tools, and mobile-friendly labels in the search results. This seems to go beyond the broken mobile site penalty Google had in 2013. It also seems to go beyond having problems with your mobile-friendly site – where it is targeting this communication to sites that are knowingly not mobile-friendly. Get the full story at Search Engine Land