Not sure on what the mark means but most of these that I have seen have some type of damage. I have a 32 inch that the main bar is bent near the upper jaw. I also have a 48 inch that has been welded all around the top jaw where it meets the main bar. They both still display I don't intend to use either one.
1930, the key lock, locks the adjustment and lower jaw assembly in place. There are 2 different positions on the main bar that are notched to set the adjustment assembly into, the key on the back side (wedge) locks the lower jaw and adjustment assembly into position.