On the previous page, you can see the unofficial SOG symbol and its flash version for the combat uniform. Note that Trautman wears the same beret that the skull in the SOG's symbol does. Rambo and Trautman surely belonged to the SOG.
Most of MacVsog soldiers came from the Fifth Special Forces that at the time used to train men in Fort Bragg, just like as the movie says. Another piece of evidence is the green beret worn by Trautman himself, sporting a Fifth Special Forces flash.
The SOG (which were the MacV special forces teams) were soldiers specially trained to run illegal missions inside neutral countries or behind enemy lines, sometimes even disguising themselves wearing Vietcong clothes.
They were used to move inside hostile territories and avoid contact with the enemy, which in most cases would have showed up in larger numbers and so, it would have turned into a death sentence for soldiers.
During those kinds of missions, their survival was mostly based on their skills in avoiding detection.
In other words, when we see Rambo hiding and avoiding the police in the woods, he is doing something he had spent years training for.
The existence of SOG teams was denied by the U.S. Government until about ten years after the war because their missions were against the international rules of war.