Very interesting gun and story. It seems unusual to me to place notches on steel like that; you can see what a mess it makes. It is much simpler and neater to notch the handles. Each notch is an X, perhaps? Weird.
My Model 28 has 42 notches around the butt (target grips) and I made each one with a few strokes of a hacksaw. Each notch is for a deer. I shot the last one in 2012.
Just because a gun is notched doesn't mean it was used to shoot somebody.