So, In Mavericks, you can set text to be displayed on the lock screen by checking the box: System Preferences > Security & Privacy > General > "Show a message when the screen is locked", then clicking "Set Lock Message..." and entering the desired text.
My problem: I want to do this to dozens of Macs by sending them a script.
Now, I found that I can set the text to be displayed with this command:
sudo defaults write /Library/Preferences/com.apple.loginwindow \ LoginwindowText 'Enter desired text here'
But, I cannot figure out how to check that "Show a message..." checkbox via either a script, an MCX setting, or a Profile.