Those look like unit type identifiers that would be used on a map overlay.
But they don't appear NATO.
The underline in the second is what makes me think this.
A rectangle with one slash is CAV. Crossed slashes is Infantry. A oval means tracks. So added to the original boxes means mechanized CAV or mechanized infantry.
I don't know if the AF, Navy or Marines use the same, but I'd think they would.