I remember very well when this was done. In the 1970s our Police Department devised a program where you could borrow an engraver from them, then mark all your belongings with your Social Security number. The idea behind this was that if someone stole the item and tried to sell it, anyone could figure out who it belongs to. My mother went around the house putting my dad's Social Security number on everything of value that we owned!
How ironic is this? Now we protect our Social Security number like it is gold. Those same thieves can use it to steal your identity. They can apply for credit in your name. A lot of damage can be done with this information. But back in those days you were encouraged to share that number with the world, courtesy of your local police department.
Funny how things change.