Related to this question, how do I go about implementing said warning banner on a gnome based Fedora 11 or Fedora 12 installation? I only care about the graphical login. I used the NSA guide to implement the banner in Fedora 10 and it worked just fine, but it appears that the gdm login screen is using a different format. I need to do add this to remain compliant with company IT policy.
You'll need to place the message in GDM's config file.
There are some instructions for different OSs here.
Fedora 11 and after:
Now, if you log out, you'll see the warning banner message just below the computer name in the login dialog. It will be center justified, but this can be changed. The dialog appears to resize for the text, so you can use more than one line of text as the message.
To change the justification of the text, you need to edit /usr/share/gdm/gdm-greeter-login-window.glade. Look for the text box id'ed "auth-banner-label". The justify tag is fairly obvious, just use the rest of the xml as a guide to see what to change.
Before Fedora 11:
This works for Fedora 10 and RedHat EL5. It doesn't work for Fedora 11 or Fedora 12 though.
Obviously replace "INSERTBANNER TEXT HERE" with your banner and a-theme-name is the name of the theme that is being used by GDM.