Pick the Americans

Does it have something to do with their gear or insignia, something that has remained constant throughout the years?

Bingo!  The Americans are the ones with all their gear on.  It is still the same way today.  I will never forget going through Doha on my way to R&R from Iraq and despite the fact that I had turned my weapon and ammo in in Iraq before getting on the C-130 to flu to Kuwait all of us Americans had to keep our full combat gear on in an area where there was absolutely no combat going on and it was well over 100 degrees.  The Brits doing the same thing as us were wearing soft caps and no gear.  The same thing happened in Bosnia in 96.  As a matter of fact in the mid-90's when I was in 1ID in Germany, we were not allowed to wear our gore-tex jackets in garrison because too many of them were getting damaged while working in the motor=pool and the commanding general decreed that we could only wear them in the field.  The American army is known for a boneheaded insistence on nitpicking crap like that.

I have slept with my boots on while deployed more often than I care to remember.

Combat codpiece !The latest piece of high-tech kit...http://www.bbc.co.uk/news/uk-12014274

That's pretty funny. 😀