By christian names. Hindus mostly look alike and you can't figure out someone's caste by just looking at them. People usually ask for your full name to figure out your caste and if you give them a christian name, they usually understand that you don't have caste. Usually names are the first things everyone exchanges, so people don't end up learning that I am christian later. I am fair and tall ( 6 ft ) so that also works in my favour.