National Guardsman in airports were carrying M16A2s, also sans magazine.
Made a great object lesson for my kids.
I had a quite different experience. I flew into Richmond International Airport (Byrd Field to the old-timers) and walked past a National Guardsman (it was an E3 or E4, I don't remember, but it wasn't an NCO) with a magazine inserted, weapon off safe, and his finger on the trigger.
About a half-second later, it was fixed.