I don't know why people use that P word to describe people from India, Bangladesh, Bhutan, Burma, Sri Lanka, Nepal.
Can you tell by sight? I can't, no more can I tell if a person is English, Scottish, German, Belgian or French.
I have no idea why Indians are called P***s. Indians are mainly Hindu or Sikh (can be other religions including Christian) whereas Pakistanis are mainly (but not all) Muslim.
The politics of Pakistan are extremely complicated, especially since the enforced division from India.
It is wrong to confuse Pakistanis with Indians or Bangladeshis. They are each distinct and to label all as P****s merely shows the users ignorance.