How to change the Mac OS X Login Screen's welcome message
The Mac OS X Login Screen displays no welcome message by default, but you can add a message such as your company name by using the commands below.
To change the Login Window message, open a new Terminal window and enter this command:
sudo defaults write /Library/Preferences/com.apple.loginwindow
LoginwindowText "www.geekology.co.za"
To revert the change, open a new Terminal window and enter this command:
sudo defaults write /Library/Preferences/com.apple.loginwindow
LoginwindowText ""