From the following link:
Windows 10 Technical Preview Build 9926 hands on -- making good on earlier promises
"While you're tinkering with the registry, you might also like to know that there's also a hidden logon screen that you may like to use instead of the default one. Navigate to HKEY_LOCAL_MACHINE\ SOFTWARE\Microsoft\Windows\CurrentVersion\ Authentication\LogonUI\TestHooks and change the value of Threshold to 1. If you change your mind further down the line, just change the value back to 0."
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Haven't tested this yet myself, but the link does show a screenshot of the login screen in question. I will test this out next chance I get.
Windows 10 Technical Preview Build 9926 hands on -- making good on earlier promises
"While you're tinkering with the registry, you might also like to know that there's also a hidden logon screen that you may like to use instead of the default one. Navigate to HKEY_LOCAL_MACHINE\ SOFTWARE\Microsoft\Windows\CurrentVersion\ Authentication\LogonUI\TestHooks and change the value of Threshold to 1. If you change your mind further down the line, just change the value back to 0."
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Haven't tested this yet myself, but the link does show a screenshot of the login screen in question. I will test this out next chance I get.