From what I know. WABCO, standing for Westinghouse Air Brake CO, tried their hand in the locomotive horn market dominated by Leslie controls and later on with AirChime 1930s. If you want to read more on them here's a site that should help you
http://atsf.railfan.net/airhorns/index.html
scroll to which ever horn you choose.
Here's the direct link to the AA-2
http://atsf.railfan.net/airhorns/aa2.html
As for value, depends. I've seen them go for at little as $100 and for as much as $500.
Great find there. I love the sound the AA-2 makes. WABCO had some very nice sounding horns in their line. too bad they weren't as popular as Leslie or Nathan AirChime horns became (not that I mind either manufacture).
If your co-worker is looking to get rid of it, let me know, I'd be glad to give it a home among my other locomotive horns.
EDIT: forgot to mention the snow cones over the bells are aftermarket add ons. They were likely added on by the railroad that formerly owned it. These are common ad ons for passenger lines, both regional and Amtrak.