More on why Nihangs wear such large turbans:

Another part is: During a point in a battle a detachment of Sikhs carrying the Nishan Sahib of the Khalsa was overrun and wiped out by the enemy. An army’s flag is sacred and a rallying image. When concern over the loss of the flag was reported to Guru Gobind Singh he tore off a piece of cloth and attached it to his own turban. He instructed them to do the same and so raised the flag upon the very heads of his brave Sikhs.

To this day Nihang Singhs who's knowledge, words, and deeds exemplify the principals of a Khalsa warrior are acknowledged the right to wear this Farla on their Damala. According to the tradition today; it is not something that one just decides to wear one day because they want to. It is appropriate that five elder Singh's who do wear it may bestow this duty and order upon a Sikh who they deem appropriate and befitting.