You can do this trick to know if you have film loaded: I put the end box flap on the back of my cameras. If there isn't a film, I remove it.
We all have done that before. I remember when my father allowed me to use his Petri FT 30 years ago and I did just that to check if there was a film in there. Guess what: there was a new film already in there!
And congratulations on your "new" FM2! I bought a "user" FM last week. Very nice cameras. Unfortunately, mine needs a CLA as the shutter is tapering at the 2 highest speeds.