Private security is not policing. It is not the military. In fact, one of the many problems with the "Soviet Agriculture" model of policing is that with sergeants and lieutenants and all that, they adopt the role of an occupying army. I can show you a link to the daily diary of a patrol policeman from about 1900. His work was totally different than policing even after 1920.

Generally, while the Class-A or "hard uniform" is still common, most private agencies have moved or are moving to other livery such as suits and golf-tees. The uniform says a lot, much of it consequential, but too much of it misunderstood.

I posted two slide shows to SLIDESHARE.com:
Overview of security guards for data centers
http://www.slideshare.net/michaelmarotta...

Introduction to private security for data centers
http://www.slideshare.net/michaelmarotta...

The government must have a monopoly on retaliatory force. But public policing follows the Soviet Agriculture model of service delivery. Like public school teachers, public police officers may be highly motivated, but they are caught in the wrong information system. It is possible to have a constitutionally-limited government that is RESPONSIBLE for policing, but which only licenses and regulates any market entities while maintaining its own (limited) forces for supervision and enforcement. We have seen many former police services contracted out: public school crossing guards and street parking enforcement are two easy examples. Inside departments, jobs formerly held by officers - especially those no longer suited for active duty - are now filled by civilians: information systems is a perfect example; dispatch is another.

The most important difference is that as business services, private security companies seek to PREVENT problems, and to PREDICT threats.

Homeland Security in the Post-9/11 world limited some of the acceleration, but, largely, since about 1970 or 75, private security has been eclipsing public policing by 2-to-1 to 3-to-1 both in staffing and capital investment. We are already a society mostly protected by private security, and have been for about 30 or 40 years.