Strange Pin. Any Ideas?

[bigmacglenn]

Great to see another mystery solved, lol...
When I was in ROTC in the early 1980s we had smooth silver discs...
cheers, Glenn

[Walkwolf]

This insignia always reminds me of Star Trek.........!

[avenger]

I believe those are called "pips".

[Walkwolf]

As mentioned in the link, it is likely pre-war or WWI era
where this type of pin/catch arrangement was used.
A lot of metal US insignia at that time was made
to look like bullion.........