U.S. Park Police

The United States Park Police is one of the oldest uniformed federal law enforcement agencies in the United States. It functions as a full-service law enforcement agency with responsibilities and jurisdiction in those National Park Service areas primarily located in the Washington, D.C., San Francisco, and New York City areas and certain other government lands. Wikipedia*

On the C-SPAN Networks:
U.S. Park Police has hosted 2 events in the C-SPAN Video Library; the first program was a 1993 News Conference.