The demonic sigil is featured heavily in the Shadow of the Storm quest. The player using it must chant a combination of the words as shown in the Demonic tome to summon the demon Agrith-Naar. If a player does not take the sigils provided during the quest, more can be made by using a silver bar on a furnace with a Demonic sigil mould in their inventory. This item cannot be made after the quest is complete, even if the player still has the mould.
Although, after the quest is complete you can use the emote to chant using the Demonic Sigil, chanting the five words in any order you want. This has no effect and does not summon demons, even if you use the right order.
While the item is only made of silver, there is an unexplained black colouration on some of the sigil.