Uncut hair is the first of the five kakars and the most visible. It is not a symbol of anything in the doctrinal literature; it is an acceptance of the form given, and a refusal to alter it.
It is what made Sikhs identifiable in the eighteenth century when there was a price on their heads. Bhai Taru Singh Ji was scalped rather than cut it. That episode is the reason the kesh carries the weight it does.
The turban is not itself one of the five kakars. It is required in practice as the covering for the kesh, and its form varies: the Malwa and Majha styles, the Patiala shahi pagg, the round dumalla of the Nihangs, the pothohari style.
Turban cases have been litigated in a dozen countries: motorcycle helmets in Britain, hard hats in Canada, school bans in France, airport screening, the military. Most have been won and several are still running.
Sikh men in the diaspora are frequently attacked after any incident involving a bearded man in a turban anywhere in the world, and Balbir Singh Sodhi was murdered in Arizona four days after 11 September 2001 for exactly that reason.
The hair is not cut anywhere on the body and it is kept covered, and it is the kakar that cannot be taken off or set aside for a day.
It is also the one that is visible, which means it carries the cost. Sikh men and boys abroad have been attacked, refused work and bullied for it for over a century.
The turban is not itself a kakar. It is the covering the tradition settled on, and the argument about whether a Sikh who cuts their hair is still a Sikh is as old as the requirement.