Is there any visible sign that the girl has had a sex before?any liquid secretion or anything from female body?

Just one sex test: There is one "test." You just ask the person (but be sure you have a reason to ask). A girl can ask a guy how many people he has had sex with. Likewise, a guy can ask a girl how many people she has had sex with. This test has better accuracy when guys are being asked, because there is more negative stigma for a girl to have had several sex partners. To be fair, stigma should apply equally to guys.