I'm not Indian but my understanding is that you can typically tell someone's caste by their last name. I'd also imagine there'd be a host of cultural information that would be hard to fake, like knowing certain prayers or rituals. Brahmin's are vegetarian, so you'd have to only eat vegetarian at the office to pretend to be one. I even had a friend who told me his sub-caste had their own secret language they spoke.
It needs to be mentioned that casteism is less of an issue in the major urban areas and in South India. In these places it is possible to grow up and live your entire life without having to deal with caste, and Bengaluru is of the biggest urban areas in South India.
