If you’re a Dalit, you’d know. As I mention in the post, membership to a caste is granted by birth. If both your parents are Dalit, you’re a Dalit too.

How do others know: it’s not obvious. Dalits either change their last name to something common enough to not have any caste indicator. They’d avoid any discussion on caste. So effectively, they hide but there are some who don’t and keep their last name. Still, not every other Indian could tell, but a more caste conscious Indian who belongs to the same region can tell. On top of it, it’s common among Indians to just plainly ask other what their caste is.