SELinux AVC Cow
Eamon Walsh talking about his XACE (labeled window) support.
The yellow bar near the bottom of the screen is always on top and indicates the security label of the window in current focus, with color coding. Each application window is also similarly marked.
In the photo above, a simulated attempt to snoop another application's keyboard via X is prevented by the XACE SELinux policy.
The AVC (security alert) is being displayed via xcowsay.