The famous band that Rambo wears is not fictional and he wasn't the only one that used to use it.
It was commonly used in Southeast countries to work and the Americans used it too.
When a soldier runs a mission in a dangerous place - as high mountains or the jungle - the best way to survive is adopting some local customs.
Even if in war movies you don't see it very often, the truth is that it was popular between US soldiers, and even more between Special Forces soldiers.
These two books show, in their cover art, stills of green berets at the time.
