I've seen similar ammo in 7.62x51 that was loaded in Cold War era Czechoslovakia. Was simply stamped 7.62 and year of manufacture, but that was Berdan primed.
I've encountered similar 5.56 brass at my range that was fired by LE. Packaging was also plain, brown cardboard simply marked M193 with no manufacturer given. Wonder if this was a special LE practice ammunition contract or military second (somebody messed up the headstamp machine that day)? This ammo was likely Federal Cartridge as the factory is in the same county as the LE range, and that department uses all Federal made ammunition, but the date on the brass I encountered was late '90s. It really could be almost anything, unless somebody has encountered this specific stamp from a known source.