The U.S. Park Police is stationed in only three locations. San Francisco (Golden Gate National Recreation Area), New York City [Jamaica Bay and Staten Island Units of the Gateway National Recreation Area (GNRA), as well as at the Statue of Liberty/Ellis Island National Historic Site] and Washington, D.C. The National Park Service oversees the agency, but also has their own daily law enforcement presence at all but the very smallest units, most of those in the eastern U.S. There are law enforcement rangers (Division of Visitor and Resource Protection) at all three of the above locations. It is hard to answer your question because I don't know the location of what you are hearing. I think the U.S. Park Police have a different type of unit/personnel radio identifier system, but I've forgotten what it is.
