Glyph of the Abyssal

Glyph of the Abyssal is a cosmetic warlock glyph that would cause the player's Summon Infernal to summon an Abyssal instead. It doesn't seem to have been implemented.

Source
This item likely would have been created using Inscription (1); taught by Technique: Glyph of the Abyssal, which has no known source.