Setting a lock message on your login window with the terminal (Mac OS)
Apple provides step-by-step instructions to set a lock message on the login window of your Mac. This spot is very useful to display a company policy or your personal contact details if your laptop is lost.
The lock message can also be configured using the terminal, which is very useful for company wide deployments. Simply run the command below with whatever text you would like to set (line breaks are supported):
sudo defaults write /Library/Preferences/com.apple.loginwindow LoginwindowText "This computer is attached to an Apple iCloud account and valuable if lost.\nPlease return by emailing email@example.com."