How are Dalits identified in India? Is it by their family names? If you convert and/or change your name and move out into a large cities of India - who can identify you as a Dalit or non Dalit.
The thing is that the upper class hindu extremists they classify them for their own gains.
Of course u cannot tell by just looking at them its not possible but often they are lowest on the economic ladder and often they work where they grow up so its easy to find out.
But its a good question i must say.