Antagonisms experienced by the Indian Sikh diaspora are usually a result of their being mistaken for Muslims, a tenuous situation since the terrorist attacks of September 11, 2001. Because turbans (albeit, head garments very distinct from those worn by pious Muslims) and beards (another similarity between Sikhs and many Muslim men) are a fixture of the male Sikh populations of the world, they are frequently mistaken for Muslims and physically and/or verbally attacked, especially the 280,000-500,000 Sikhs residing in the United States. Islamophobia, then, represents the single greatest threat to the safety of Sikhs throughout the Western world. Also, the Sikh religion is very distinct from that of the other monotheistic religions, especially its belief in the Ten Gurus as secondary figures to the one Supreme Being. Simply being different, in too many communities, is sufficient to provoke hatred and fear, and Sikhs are no exception. That said, Sikh populations outside of India are generally prosperous and successful in the myriad professions in which they participate.
If Sikh populations among the diaspora are generally targeted because of their physical similarities to Muslims, the latter identified with the proliferation of terrorist incidents around the world, the Sikh population in its native Punjab region of western India experiences a very different kind of challenge. India, a country of over one billion people, has a native Sikh population of about 19.2 million, according to that nation's census figures [See: http://censusindia.gov.in/Census_Data_2001/Census_data_finder/C_Series/Population_by_religious_communities.htm]. That's a small minority in a country dominated by well-over 800 million Hindus and 138 million Muslims. While Sikhs are well-represented in many Indian institutions, including the Armed Forces, where the number of Sikh officers is well-above that community's proportion of the total population, there are tensions between Punjabi Sikhs and the other major ethnic/religious groups. A Sikh independence movement, known as the Khalistan movement, had waged a violent, and obviously unsuccessful push to secede from India during the 1970s and 1980s, with the movement's leaders complaining of institutional and wide-spread discrimination at the hands of the majority Hindu and Muslim populations. Currently, however, that independence movement is a minor irritant to the nation's government, especially in the wake of the years of Sikh politician Manmohan Singh's period as India's prime minister from 2004 to 2014.
Returning to the issue of diaspora Sikhs, the kind of prejudicial behavior that has frequently reared its head with respect to other ethnicities will likely continue to target Sikhs if for no other reason than that they look different than the populations of the nations to which they migrated over the years. Unfortunately, that's about all it takes, racial and religious prejudices being based in most instances on superficial characteristics, and turbans apparently qualify.