A police officer's badge number serves the purpose of identifying the officer to the public, according to Slate and the District Department of Transportation. The badge can also serve a ceremonial purpose, such as when police departments retire the badge numbers of slain officers, notes The New York Times.
Many police departments, such as the New York City Police Department, require officers to wear a badge, tag or label containing their name or identification number, according to Slate. Although not many states require this by law, some states, such as Massachusetts, do. The Washington D.C. Police Department has been criticized by the Police Complaint Board for its officers frequently failing to identify themselves to suspects and witnesses when requested, according to the District Department of Transportation.