Show User Notification from Package or Task-Sequence
From the archive (2010). Written for the tools of the time, so some details may be out of date.
Credit to Roger Zander for this nifty trick.
A way to show a simple user notification message from a Task-Sequence or a Software Package is to use the following command (as one line):
powershell.exe -command $a = New-Object -comobject SMSCliUI.UIEvents; $a.ShowMessage(‘User Notification’, ‘Please restart your computer…’, 1)
The message will be visible even if the package runs with System privileges and the flag “Allow users to interact with this program” is not enabled.