Most medical helicopters use a portion or all of their aircraft registration number as identification.
When communicating with air traffic control, you should hear N102AM (for example). Some pilots may abbreviate the callsign and drop off the "N" prefix.
By the way, N2AM is a fixed wing plane. Maybe you missed another number? Or, maybe this medevac flight was fixed wing???
As to which bird, it would be anyone's guess. If you really want to know, go the internet and search for EMS air ambulance providers in your area. Many company websites will post aircraft pictures and list aircraft registration. There is a FAA search engine for aircraft registration but that would take forever looking for "----2AM." If I had to guess, this may be an Air Methods aircraft.
