In any version of OS X starting with 10.7 Lion, you could set up a custom message to display at the bottom of the login window, which would appear when they’re logged out, wake the Mac after sleep, or the screen saver begins. The message could be a simple greeting, like “welcome back”, a password hint, like “my wedding date”, or even your contact information in case that one day you misplace or lose your Mac.
So, how to set the login window message? You can finish the task quite easily.
You can leave any information in the custom lock screen message without word limit. To remove the message, just uncheck “Show a message when the screen is locked”. If necessary, click the Lock icon to prevent the further modification in this pane.
After saving the change, you can lock your Mac screen by choosing Apple > Lock Screen or through the Control – Command – Q keyboard shortcut, to test the new Lock Screen message. It would be displayed beneath the user account in the login window.
For Mac geeks, they can apply a Terminal command to do the trick as well.
So that’s how to set a custom message using Terminal. Also easy to perform, right?
To revert back to the default value of no message being displayed, run the command:
sudo defaults write /Library/Preferences/com.apple.loginwindow LoginwindowText “”