[fuzebox40]

Remove the left side grip to reveal the serial number and letter code. This is required for dating as well as caliber and is it a top break or solid frame.
Notches like that are not uncommon as simply to identify ones personal weapon. Sometimes you'll see something similar on the grips, both sides, as to be spotted from either side of the gun.
This is not to say that it hasn't been used to kill someone. It may very well have a higher body count than Clyde Barrow. But probably not!