From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Police (警官, Keikan; Literally meaning "Cop") enforce local law.
The police were all very similar to their real world counterparts. Their main purpose seemed to be protecting single cities and towns that did not require the work of the other two military groups. Their weaponry and such was more limited as they only had the use of smaller guns, bazookas, etc. As far as their transportation, they used scooters, motorcycles, and a variety of police cars.
They seemed to have ranks that were all from the real world, such as sheriff and chief, and sometimes used wanted posters. The uniforms were near-perfect replicas of the real world police, with the use of hats, helmets, blue uniforms, handcuffs to arrest the opposition, and occasionally a microphone to give speeches. The police in the Dragon Ball universe were rarely if ever shown using animals in their squads, and in fact some were anthropomorphic animals themselves.
The police were seen many times in the series attempting to arrest and sometimes even kill the villains, however, they always failed and usually were killed or injured in the progress.