The Mortal Instruments: Runes meaning
Runes, also known as Marks, are symbols that grant beings various supernatural abilities, with both angelic and demonic runes known to exist. For Shadowhunters, runes are a complex runic language given to them by the Angel Raziel, which grants them powers beyond those of mundanes. Runes are burned into Shadowhunters' skin using steles, and are their most common tool in their fight against demons.
Runes are markings given to the first generation of Shadowhunters by the Angel Raziel to assist them in fighting the demons they were tasked to eradicate. Every rune that is accessible to Shadowhunters is recorded in the Book of the Covenant, and have also been copied into the Gray Book, which is a specially crafted book with each rune placed in its pages. Copies of the book are rare because each book must be specially made, due to the fact that steles, made of the holy metal adamas, burn normal paper.
The first ever recorded Mark was the biblical Mark of Cain, set upon Cain, which protected him from harm, as any harm against him would result in the same harm rebounded upon the assailant sevenfold.
In 2007, a large number of Shadowhunters were forcibly Turned into demonically-aligned Dark Shadowhunters with the Infernal Cup by Sebastian Morgenstern, which resulted in their angelic runes fading from their skin. After being Turned, the Dark Shadowhunters were only able to apply demonic runes.