Sumi

The Sumi are a tribe of people, where most of women have a special tattoo on their left arm for religious reasons.

Background
The women in the Sumi tribe that have a special tattoo on their left arm is symbolic of their betrothal to god and their vow of chastity.

Hunter Exam arc
After Kurapika saves the navigator's wife from the Kiriko disguised as Leorio, he immediately demands to know who she really is. It's later revealed that the navigator's wife was really also the daughter in the Kiriko family. She discloses that Kurapika instantly recognized the tattoo she had as one from the Sumi tribe. This would make her marriage to the "Navigator" null and void as she took a marital vow towards god.