You definitely cant tell whether someone has an STI by looking at or talking with them. In fact, most girls and about half of guys DONT get any symptoms so they dont even know that they have an STI! Symptoms for girls can include burning or pain when passing urine and unusual discharge from the vagina.

What are the signs of STD in a woman?

Women may experience the following symptoms:Burning or itching in the vagina.A discharge or odor from the vagina.Pain around the pelvis.Bleeding from the vagina that is not normal.Pain deep inside during sex.Sores, bumps or blisters in the vagina, anus, or mouth.Burning and pain with urine or with bowel movements.More items