—From Codex entry: Vallaslin: Blood Writing
Vallaslin, sometimes referred to as blood writing, is what the Dalish call the intricate facial tattoos worn by all adult clan members. The ink used to do so is considered sacred. Many young Dalish receive their vallaslin when they are around 18 years of age, or so. When a Dalish elf comes of age, they prepare to gain the vallaslin by meditating on the gods and the ways of the Dalish, and by purifying the body and the skin. When the time comes, the Keeper of the clan applies the blood writing. This is done in complete silence. Cries of pain are taken as signs of weakness. If a young elf cannot tolerate the pain of the blood writing, they are deemed unready to undertake the responsibilities of an adult. The keeper may stop the ritual if they decide that the one gaining the vallaslin is not ready. Blood writing is at least in part a religious practice, and there are different designs representing deities in the Elven Pantheon. There is no design for Fen'Harel.
According to Solas, the use of vallaslin during the time of Elvhenan is a much more controversial concept than believed by the Dalish. He reveals that, in the days of Arlathan, the tattoos were not signs of patronage to the various elven gods but, in fact, slave markings--signs of ownership--when noble elves enslaved the lower classes; they were representations of the gods that the nobles favored. Abelas and the Sentinels of the Temple of Mythal have vallaslin dedicated to Mythal etched on their faces.
Through cultural reappropriation, vallaslin is now something entirely different for the Dalish, who utilize the markings as something positive for their people.A text on the carved tablet found in the Temple of Mythal tells of "the eventual failing" of elven markings.
Thus far, three groups of Dalish have been encountered: those of the Dalish Elf Origin, those of Zathrian's clan in Nature of the Beast, and the ones found in the Exalted Plains in Dragon Age: Inquisition. Various designs of blood writing can be seen on their faces. There appear to be eight main designs, each of which comes in a simpler and a more complex version. Though similar to the main eight there are two unique designs that are used by Velanna/Seranni in Dragon Age: Origins - Awakening and Merrill in Dragon Age II.