Earlier last year Google released Hummingbird update to its search algorithm updates and also released set of Checklist for Mobile Website Improvement. Google recently started testing a feature for its mobile search result page by showing mobile friendly or mobile non-friendly icon alongside the website address. Below is the screenshot of a Google search result page on iPhone using Chrome that shows mobile friendly site icon before the website address.

Google also displays non-mobile friendly icon for the non-mobile friendly websites in the SERPs. This icon in the mobile search results that symbolize when a search result links to a page that is not mobile friendly.