Yesterday I talked about adding a small amount of system information to the login screen in mountain lion. This afternoon I have been doing a bit more digging and have two more techniques. One is to add a message to the bottom of the screen. The second is a login window banner, most notably to be used as a policy banner in which users can accept the terms of using that Mac. They are only simple changes but add a certain amount of functionality, especially if you need them.
If you want to add a login message to your login window in mountain lion you have to change the right preference. Open up System Preferences in your Applications folder. Open the Security & Privacy preference. Yo will notice that there is a check box that allows you to show a login message. Check this box, then press the button to open up a small editable text space. If the check box is locked out, press the lock in the bottom left corner.
Type what you want in the text box. I recommend you keep it shot. When you are finished press the OK button. Now when you go to your login screen you will notice a small message above the shutdown and restart buttons.
A policy banner is on you typically find on a school or work computer. It allows the administrator to set a range of guidelines and rules for the user to follow. The first step is to right your message, using either TextEdit or a suitable word processor such as word or Pages. You can add in images and colourful text as needed. Ensure you save the file as a .txt, .rtf or .rtfd file. Change the name to PolicyBanner, taking note of the capitalisation.
Then move the file into /Library/Security folder on your Mac. If you want to find this folder please see a previous post, discussing this issue. Now, every time you go to your login window, you will see this policy banner.