Oh, yeah, dis gon be good.
Those numbers at the top are soundtrack cue numbers. “1" indicates reel one (this dates back to when movies came on film and had to be broken up on separate 1,000-foot long reels; today, digital movies are broken into separate “reels” of any arbitrary length). “M” stands for music (as opposed to sound), and the third character is just a chronological order of the cues. So this is the very start of the movie: Reel 1, Music, Cues 2-4. Don’t ask me what happened to 1M1. That is probably just the 20th Century Fox fanfare, which is not numbered in this fashion in this score.