Some help ID'ing civilian choppers in the US. List is far from complete.
Some suffixes often associated with medevac choppers:
AM = Air Methods (an owner's name)
PH = Phi Air Med (an owner's name)
ME = MEdevac
MT = Med transport
LF = life flight
ER = emerg room
RX = med
MH = med helicopter
I don't believe there is any formal requirement to use specific suffixes for medevacs; it's whatever the owner picks or can get. Glance down this list at the ones marked EMS and those are confirmed medevacs. Those not categorized in the list haven't been ID'd yet.
It's apparent that medevacs are not limited to Eurocopter 35, 135 or Lakota; other models are also in medevac service.
On ADSB, after clicking a chopper of interest, click the Flightaware link (CTRL-click to open a new tab if tracking many). Flightaware will keep tracking that specific chopper while you look around. You can set the map to satellite and zoom in and actually see if it's landing in a neighborhood, on a freeway, or in a hospital parking lot (well you can guess anyway). You can also scroll down below the map and see its recent flights; if medevac you may be able to determine where it's based (usually a regional or municipal airport) and whether it does fly to/from a hospital. Photos of the chopper can be helpful to determine if it's an air ambulance/EMS.