Customers running Win 7 SP1 or Win 8.1, who have not yet scheduled an upgrade till date, may start seeing a full screen notification as soon as they unlock their PC :

KB 3163589 “Your PC is running an outdated version of Windows” notification

KB 3095675 : Windows 10 upgrade: How-to information on scheduling and notifications

KB 3164060: How to manually decline the free Windows 10 upgrade offer from the Get Windows 10 app

KB 3173040 : Windows 7 SP1 and Windows 8.1 End of Free Upgrade Offer Notification