Like Malcolm X we use the initial letter of our parents' names. But we attach it to the beginning of our names. It is called our initial. For instance, I was D. Rajalakshmi, as my Dad's first and only name was Desikan.Some people use only the initial. Some people expand the initial to their father's name, while filling up forms, which means that to a westerner, it looks like your father's name is your first name.
While people create facebook accounts, they are reluctant to mention their initials. So they break their names into two parts.Since old timers like me have long names anyway, its easy. I call myself Raja Lakshmi. And those who have short names just use their names twice. (Varun Varun/ Latha Latha) and so on. When I travel to other states, I realize that although we Tamils feel awkward about having initials an single names, it was a pretty good idea to get rid of caste based surnames.