That’s a safety notch analogous to half cock on older guns. Essentially if you ever carried condition 2 you would have a way to store the gun with a live round in the chamber and the hammer down-ish.
Then cock it with your thumb and if you screw up and drop the hammer the notch (in theory) catches the hammer and prevents you from blowing a hole in something.
It’s just as much a holdover from WWI when they were trying to give soldiers a convenient way to restrike a dud round in a semi safe way.
That’s a safety notch analogous to half cock on older guns. Essentially if you ever carried condition 2 you would have a way to store the gun with a live round in the chamber and the hammer down-ish.
Then cock it with your thumb and if you screw up and drop the hammer the notch (in theory) catches the hammer and prevents you from blowing a hole in something.
It’s just as much a holdover from WWI when they were trying to give soldiers a convenient way to restrike a dud round in a semi safe way.