Columbia subject headings:
Crime prevention--United States--Equipment and supplies.
Police, Private--Licenses--United States.
Police, Private--United States.
Private security services--United States.
Harvard subject headings:
Crime prevention--United States--Equipment and supplies.
Police, Private--Licenses--United States.
Police, Private--United States.
Princeton subject headings:
Crime prevention--United States--Equipment and supplies.
Police, Private--Licenses--United States.
Police, Private--United States.
Private security services--United States.