I'm not very knowledgeable on the subject but IIRC the Sikh don't cut their hair as part of their religion and the turbans are a strip of cloth that gets folded around their hair and then it is wrapped around their head and tied tight. It doesn't seem like something that would fly off from the wind, although depending on how you crashed it could slide off your head easier than a standard helmet. I think the real question is how much would a couple millimeters of non-newtonian fluid do to reduce a motorcycle impact.