User blog comment:VedranTheII/Pretentious Diaries 2: What tricks would you teach your Aura?/@comment-10380701-20150718080559/@comment-9464517-20150718102405

Also because runes are often used in fiction to display something old and mystical, and are closely tied to symbols of magic. Since Cinder and Glynda are both pseudo-witches, this seems very likely indeed.