The Vietcong were 'armed civilians', in other words guerrilla fighters, with no uniform.
Their ranks were made by men, women and sometimes very young kids too. They used any clothes while fighting and when at risk of capture, they used to toss away their weapons, hoping to be mistaken for civilians by the enemy.
The Vietnam War caused so much civilian deaths also because of this fighting attitude.
On the right, one of the very few garments the Vietcong used very often: the so called 'black pajamas'.
Lacking the use of uniforms, the black pajama was the only easily available 'low visibility' dress for the Vietcong.
The scarf (called 'khan ran') represented the soldiers rank.