Somewhere on the frame.
Early firearms in .22 caliber were not required to have a serial number. Your Marlin 81 falls into this time frame.
Take it to a gunsmith
Rifle? Handgun? Caliber? Maker? Other markings?
Impossible to say without a more detailed description of the handgun in question.
Many .22 caliber rifles made before 1968 did not have serial numbers. This would include your Marlin 100.
1975.
1980
Your marlin 336sc(standard carbine) was made by the marlin firearms company in 1950.
Impossible to answer without the exact model and caliber.
This Marlin 39A Mountie .22 Caliber Lever-action rifle with serial number R5077 was manufactured between 1957-1958.
Impossible to tell from just the serial number.
The J prefix to your serial number indicates that your marlin model 39A was made in 1952.