Earrings throughout history have been worn as clip on's, ear cuffs, stick-on's, ear hooks and ear plugs. Most types of earrings are removeable however some are permanent.
An earring was often put in one ear, as a sign that a person was a slave, in ancient times. In the early days of America, pierced ears were a sign of an immigrant, so clip on earrings where preferred. Now no prejudice exists.