After accessing the administration menu and then re-entering the media player application, sometimes the menu bar on the bottom will not disappear.
Plug a USB keyboard into the media player.
Enter the administration menu and then exit the application.
Once you have exited the Wondersign application, relaunch it or wait for Wondersign Manager to do so. This will restart the Wondersign media player without the Android menu bar at the bottom of the screen.