Traffic police
Traffic police direct traffic and enforce the rules on the road. Their signals apply to drivers and pedestrians alike, and a police signal overrides a traffic light - if an officer is directing at a junction, do what the officer says.
If you are stopped, stop properly, and be civil. If you were in the wrong, acknowledge it politely. Arguing that you did nothing wrong, calling other drivers as witnesses, or driving away all make the situation worse and are themselves offences.
Police may act on the spot for driving without a number plate, driving under the influence, and driving on the wrong side of the road.