Almost from the moment, some five centuries ago, that their religion was founded in the Punjab by Guru Nanak, Sikhs have enjoyed a distinctive identity. This sense of difference, forged during Sikhism's fierce struggles with the Mughal Empire, is still symbolised by the ""Five Ks"" (""panj kakar,"" in Punjabi), those articles of faith to which all baptised Sikhs subscribe: uncut hair bound in a turban; comb; special undergarment; iron bracelet and dagger (or kirpan) -- the unique marks of the Sikh military fraternity (the word Sikh means ""disciple"" in Punjabi). Yet for all its ongoing...