In all previous versions of Windows, the screen that appears when a user locks the computer AFTER logging in is different than the screen that appears when the user has not yet logged on or has logged off. In Windows 10, both screens look exactly the same, and if the user changes the so-called lock screen (the image that appears BEFORE the login screen or the screen to unlock the computer), it changes for BOTH logging in AND unlocking a computer that is logged in. The actual state of the computer in the two cases is actually different. Many programs that are started during a login session continue to run when the computer is locked, and even Scheduled Tasks that are scheduled to start at a time that the computer is logged in and locked WILL start, but if the computer is logged off, they will not. Is there any way to change the appearances of either of the two screen that ask for a username and password (the unlock screen and the login screen), so that someone can look at the screen and determine whether it is logged off or locked?
There are separate "lock screens" and "logon screens" in Windows 10. You can set the Lock Screen with "Lock Screen Settings" under Personalization in Settings. (See https://support.microsoft.com/en-us/help/17185/windows-10-lock-screen or https://binged.it/2ORvMx8 )
The Logon Screen can be changed through Group Policy or a Provisioning Package, at least in the enterprise SKUs. See https://docs.microsoft.com/en-us/windows-hardware/customize/enterprise/custom-logon.
You might also be able to use one screen saver for the "default" (signed-out) user and one or more different screen-savers for users.
I think if you tweak these settings you can get the visual indications you want.