OK, I just saw some photos of PM Singh. He's wearing a turban.
Yes and he is Sikh which is a variant of Hinduism somewhat. As someone earlier said, the Sikhs are known as warriors especially against Muslim invaders. So it is always strange when a hate crime is perpetuated against a Sikh because they are mistakenly thought of as Muslim. I imagine there is no greater insult to them than being thought of as Muslim. I am not a religious scholar.
The turban isn't determinative of whether you are Sikh. Lots of Sikhs don't wear turbans. And lots of other groups wear turbans. But if your name is Singh -- you're a Sikh.
Somebody upthread wrote that the Sikh religion was a branch of Hinduism. Actually, that is only partially true. Sikhism is a syncretistic religion, combining elements of Bhakti Hinduism and the Sufi branch of Islam. There was also something upthread about the supreme insult for a Sikh being mistaken for a Muslim. Actually, Sikhs would prefer not being mistaken for either Muslims or Hindus. There is a long standing thread of enmity between Sikhs and Hindus. (Hindus destroyed the Golden Temple of Amritsar, the holiest shrine of Sikhism back in the 80's.) The fact that a Sikh is the PM of India is a a good sign -- maybe an indication that some of the worst of the "communal" violence between the various Indian groups is over.