From Halopedia, the Halo wiki
The Utgard Constabulary was the primary law enforcement agency in the city of Utgard on the human colony of Harvest. It battled the invading Covenant during the First Battle of Harvest in 2525. Several of its members also were part of the Colonial Militia of Harvest. They donned riot armor and primarily carried M7 SMGs.
Members of the Constabulary, such members like Lars and Finn, also guarded Governor Thune's office.