US 605 On A Chinese Newspaper

Agreed, this kind of thing can make it through the mail stream. During the vast majority of the mail stream, an individual piece sees very few human eyeballs.

Mailing promotional items or other mail that is not important is probably worth the gamble (assuming a person does not have an ethical issue with intentionally using invalid postage).
Don

Hy-brasil, well that makes much more sense...!

That's some incredible detective work there Rick! I think you nailed it! The owner must have been commemorating the much anticipated return home. It's also the same date that the UN held their first meeting. Peace is being established.

I'm wondering why the stamp was necessary... Maybe it was to avoid legal ramifications, as I'm sure there's limitations to how an official postmark is used.

Here is another example of the type of leaflet found in the Original Post. This is a different one, and is printed in red on one side.




And the other side...



both have the same ship postmark, same day Jan 10, 1946.

Looks like a philatelic souvenir to me.
Mike

Special delivery stamps were service specific meaning they could only be used to pay for Special Delivery Services. Special Delivery stopped in mid 1997 as Express Mail supplanted it. If I was PMG I would allow the SD stamps to pay for priority express mail.

F1 and FA1 remain valid but service restricted, registration and certification. Airmails were service restricted until airmail was eliminated as having an extra charge.