Some of them are real gems, many are not something I would want to watch.
I have no idea what “M” is about.
“M” is a murder mystery / thriller set in Germany between the world wars. It is considered a classic of cinema techniques.
It might be the M for “Mature” audiences which was the old name for a rating of “PG”.
After the murder of Bobby Kennedy it was feared that the government might regulate violence. TV shows for adults dumbed down to kiddy shows, comic books changed their formats, pocket books removed their lurid bloody and sexy covers.
But the Movie industry said they would regulate themselves with a code system. The Government backed off.
Hot digigy dog! The HAYS code is dead! If you got them make them!
Movies were reshot to ADD sex and violence. More blood and nudity flowed from the screens.
The first movie rating was G-M(mature)-R-X.
Then G-GP(the old “mature”)-R-X
Then G-PG-R-X
Now, G-PG-PG 13-R-NC 17.