When I want to talk about the 1940s, do I use ‘40s or ’40s?

Question

The distinction was hardly visible in my question, but what I meant was this:

Is the symbol in front of "40s" an opening single quotation mark or an apostrophe / closing single quotation mark?

Answer 1

The "40s" is written as I just wrote it, or you can write the "1940s."

The apostrophe after the number is now ommitted.

Do not write, "1940's" or "40's."

Best,

Charlie