This one has to rank up there as the most often reproduced military knife on the planet. In all probability 9 out of 10 will be fakes. It is so rampant it killed the market on these knives. Take your time and study any specimen you are looking to buy. Here is the actual prototype knife made for Atlanta Cutlery courtesy of Bill Adams.
Type 1 repro
Type 2 Repro
This knife has a thinner handle and deeper swells to the handle. It is also marked U.S. on the handle, not a very high quality knife.
These knives can be found all over the place. This one is a knife you can really get taken on as so many were made all over the planet over many years it is difficult to tell which is which on just the repros alone.