Designates whether unregistered users are prompted to register their own authentication information when they sign in for ...

Designates whether unregistered users are prompted to register their own authentication information when they sign in for the first time.  This is not yet supported for Office 365 sign ins.
 
If set to "No," administrators must manually specify the necessary password reset authentication information in the properties for each user in this directory, or instruct users to go to the registration portal URL directly.