1960
Serial numbers on firearms in US were made mandatory by the Gun Control Act of 1968.
It's possible that there isn't one - serial numbers on firearms didn't become mandatory until 1968.
1992.
1954
1952
After the 1968 Federal Gun Control Act, it became mandatory. Before that, many did not have a serial number. Crime was wiped out with the serial number addition. Yeah, right.
1990
1952
1987
before graduation
In which country?
1984