The Department of Defense (DoD) login banner must be displayed immediately prior to, or as part of, graphical desktop environment login prompts.
Failure to display the logon banner prior to a logon attempt will negate legal proceedings resulting from unauthorized access to system resources.
This requirement applies to graphical desktop environments provided by the system to locally attached displays and input devices as well as to graphical desktop environments provided to remote systems, including thin clients.
How this relates to the STIG checklist: STIG vs SCAP benchmark.