In starship classification, a police vessel was a spacecraft used for police activities.
According to the Treaty of Sirius, Kzinti police vessels were the only military craft that the Kzinti were allowed to use following the Earth-Kzin Wars. (TAS: "The Slaver Weapon")
The Angosians also used shuttles that were police vessels. These police shuttles were used to transport criminals to prison. (TNG: "The Hunted")