Although this has been tested to work, in some cases there may be some issues with macOS policy banners after installing Symantec Endpoint Encryption.
When properly applied, you can add any login banner and display a custom window such as the following:
The above is a sample, and simply taking a screen capture of the doc, pasted it in the rtf document. Once deployed, the user needs to click "Accept" to be able to login to the system.
The macOS documentation should work generally as tested, but if there are some issues getting this to work, the following command may also help to get this working:
defaults write /Library/Preferences/com.apple.loginwindow.plist SHOWFULLNAME -int 1
The above command should turn on the list name. To turn this off again, run the following:
defaults write /Library/Preferences/com.apple.loginwindow SHOWFULLNAME 0