There is a bit of a difference in outward appearance, but not much. I have the USA version and the best way for me to tell that they are indeed USA is the lack of a little red triangle on the heel. Or a little metal "O" on the ankle.
The USA have a sterile outward appearance and the "O" on the ankle is pressed into the leather. Also, the tongue is just marked with the size. No tag or anything.
When I got mine I thought that they looked a bit different compared to the website so I called Oakley to ask about it. They gave me their "Military orders" number and when I called and asked the chick about them, she acted like unless I was military that I wasn't supposed to have them. She wanted to know which dealer I purchased them from and everything!! She was more than a little pissed. Strange I thought, they are just boots.
They are hard to find, but worth the money and time to find IMHO