some institutions and organizations use codes when announcing something over their loudspeakers to keep from alarming the public. here are a few:

• 'paging doctor brown' - used by hospitals to signal that there is a violent patient or non-staff person in the building.
• 'code green' - used by walmart to alert staff members that there is a hostage situation somewhere in the store.
• 'code ten' - used in hospitals to signal mass casualties. also sometimes used by other businesses to signal a suspicious credit card.
• 'code delta' - often used by cruise ships to signal a biological hazard, such as an infectious disease.