Unkown Visualization

What are those marks on my back? Scenario is: Shadow Priest, Delve: Darkway, 2 players, Valeera as DD. The AI didn't had an explanation. Claude said: no idea. Gemeni told me (hallucinated) that is is a visualization for Warlocks.
I thought I once read you had to find a play with a similar mark, but my wife's char didn't have any. And the post was Raid-related, IIRC.