Well it is a stereotype, and they are often true, but not always. eg, in TN, the average brahmin or upper class individual will be fair-skinned while the lower class one would be dark skinned.
I guess up in the North, this does not hold.
> but certain states like Tamil Nadu banned surnames for this reason.
The govt did not ban it. It was more a social movement where one was looked down upon (and even discriminated against for showing they belonged to the higher castes). That's why there are still folks who continue to keep 'Iyer' in their name.
Do you have ancestral home in Mylapore? If not you're not real Tam-Brahm. (JK obviously)
Ofcourse the Iyers and Iyengars wouldn't switch because they had more to lose than they gained from hiding their caste identity (they are the so called upper castes who have traditionally held a much priviledged position).
Nevermind that one can be "knighted" - the idea that one could be "brahminated" is no different from thinking one could be "whited" in the antebellum south. (And no, the "honorary whiteness" given to certain asian ethnicities is not akin to "whiting" - it's merely defining a subdivision of a caste to be slightly higher than the other lower castes)
Since economic mobility was greately reduced because of economic stagnation caused by centuries of invasion, they re-applied the originally profession-based caste system using racial discrimination brought to India by the Mughals and the British.
caste certificate
Generally you wont be able to figure the caste of someone but there are clues like skin color, fairer skin generally is "upper" caste, sometimes your surname also gives away your caste.
Unfortunately some Indians specially from the "upper"caste take this very seriously and think they are superior compared to other Indians.