You can now add personalized text to your Mac OS X Lion lock screen. In earlier versions of Mac OS X this feature wasn’t available for all apps , it was only available only through third-party apps or hacks. Now this feature enables you to add your contact information to the lock screen which might help you in Retrieving your Mac back if you lose it.
If you want to customize your lock screen just launch System Preferences, access the Security & Privacy control panel and click on the General tab. By default this tab is locked so you’ll need to click on the padlock on the bottom left side of the window and enter your admin password before you are able to make changes to the current settings.
Once you’ve done that look for Show a message when the screen is locked if you check it then you’ll be able to enter the text you want displayed on the lock screen. Just like in this example:
After entering my information above my lock screen now has the following displayed under the login window