New York City is a very large metropolitan city with a population of over 8,310,000 people with over 18,800,000 people living in the area around it. An extra 500,000 people enter the city during a weekday. It has many police and law enforcement officers such as; the NYPD, the (MTA) Police (that used to be called the Metro North Commuter Railroad Police), the Port Authority Police, the FBI, the Department of Homeland Security, the Drug Enforcement Administration, and U.S. Customs and others. The color of the day system is about officer safety. With so many armed officers in the city, undercover police officers need to have an easy to use system in place so that other armed officers know that they are there and do not shoot them when they use their guns. The system is also used so that a uniformed officer will not disturb a person who is really an undercover police officer who is acting as a homeless person so that criminals will rob him.