The Profound Mark, the Elder Scrolls Story
The Seditioner's Amulet is a a sort of artifact which allows the entrapment of souls, as a soul gem that may or may not be re-used (the well known aspect of Azura's Star), but also summon a Daedric Prince for an audience, one that Boethiah is slightly more likely to deign to answer.
It currently has The Dragonborn's soul. The choice which remained was to crush the amulet, thus releasing the soul, or search for some way to return LDB to life, instead of sending him towards peace.
In the possession of Nexius, but it has touched the entire party's hands. The two sensible options remaining are to crush the amulet, and release the LDB's soul to peace and rest, or to wait and hope to find a way to bring him back, which Nymaril has confirmed is possible. Didn't have a clue how though.
Was destroyed by Del to stop Loreaine from tampering with the divines themselves.