There’s no physical “proof” of virginity. The hymen is associated with virginity, but the lack of one is not proof of sexual activity as it can tear or stretch due to a variety of activities, and it’s possible for women to be born without one. The only way to know for sure what *anyone’s* sexual history is, is to ask that person. A guy has no way of knowing if a girl is a virgin anymore than a girl has a way of knowing if the guy is one.