A mark is a tattoo-like symbol that grants its bearer a superpower. The mark generally manifests itself on a person between the ages of fourteen and eighteen, often in a time of need. Once a mark has manifested, it can not be removed. If the skin on which the mark rests is somehow removed, the mark will manifest  itself elsewhere on its bearer.

People often use the term mark and power interchangeably, e.g. "She used her mark to target blend into the background."