Vietnam/Cold War Era Russian Navy Signal Flag "Й" Marked "J"

Description

Here is a Russian Navy Signal Flag. The flag is a big white swallow tail with a black circle in the center. The flag is "
Й"
which means "Found mine".
I pin it around Vietnam/Late Cold War because the material it's made out of is indicative of materials that would've been used at the time.
It is marked "J"
Shipped with USPS First Class