Originally Posted by NewGuy

The J designation was used for machines from the Singer plant
in Saint Jean sur Richelieu (some people call it St. John's), Qubec, Canada.

J - Canada
K- Scotland
G - Germany
M - I think was Spain, I'd have to look that one up. I don't have any "M's".
Of course "No letter" was used for the Elizabeth NJ, USA machines.

These are similar to "Mint Marks" on coins.
The letter just tells you where it was produced.

Long answer for short question.
Lots of times other people read these and have similar questions.

Allen