Well I wanted to know that ,how can we know that a person in front of me is virgin or not?what are da things which tell us that a girl or a boy is a virgin or not?

There is no way of telling that a person standing in front of you are a virgin or not.

Virginity is a psychological concept, not a physical state.

Im guessing that you ask them if it is that important to you?

What's unimportant about this thread, is having to know.
Who cares? Virgin or not, they can still be desirable.

Gem, virginity is not a physical characteristic, it is completely psychological, maybe even philosophical.

There are different forms of virginity, but physical is definitely one of them. There are also the spiritual and the emotional virginity. Even the psychological and the philosophical virginity.

The whole point is that you cannot tell whether a person is a virgin by looking at that person. No one wears a sign. The only definitive answer is to ask that person. Even a physical examination is not foolproof. Sex, Etc. -- Can you tell if someone is a virgin? (http://www.sexetc.org/faq/sex/719)

The easiest way is to ask them but there are no obvious things to look for.
Virgins don't have a big sticker on their head or a mark somewhere on their body , either way I don't think it matters and if it does to you then maybe you should just ask.