RentaCops in Public Spaces?

Hey... Over West Street by the former World Trade Center site there are two pedestrian footbridges. Something's been pissing me off a bit: Each of those bridges (which run over West Street--public property) are staffed by non-Cops with gray jackets that say "SECURITY". periodically, if someone goes the wrong way up an escalator or a tourist crosses a line to get a better photo, these rentaCops will whistle or shout them out of wherever they are. Is this legal? Are we really allowing private rentacops to take police functions on public property? -TD