Have forms, login fields and other input sections on your HTTP website? Chrome is going to mark them as not secure.
Google sent email notifications via Google Search Console to site owners that have forms on web pages over HTTP. These pages will be marked as not secure in Chrome starting in October 2017.
Google said, “Beginning in October 2017, Chrome will show the ‘Not secure’ warning in two additional situations: when users enter data on an HTTP page, and on all HTTP pages visited in Incognito mode.”