A digital communication system is disclosed, that allows a display of override content to interrupt a display of ongoing content on one or more display units. Ongoing content, such as advertisements, news, entertainment, or other relevant information, is provided on the display units until an urgent or security-related alert is required, and display of override content becomes necessary. Override content can include information relevant to the security of a passenger or passer-by viewing the display. Override content can relate to security threats such as accidents, major delays, fire, missing children, terrorist activity, or other content deemed adequately pertinent to warrant interrupting the display of ongoing content.