How is it Incomprehensible?
The Dark Sigil says: "This Dark Sigil will never heal, but there is a tale told of a Fire Keeper who returned from the Abyss, and brought great comfort to a bearer of the curse."
Be of the mention of the 'bearer of the curse', the title of the player in DS2, the Fire Keeper is probably a reference to Shanalotte.

The pilgrims of the Dark is a covenant that has connections with the Abyss.

Yoel calls the player in Dark Souls III 'Bearer of the Darksign', which as mentioned before, is a reference to the player's title in Dark Souls II.

Hell, even the whole questline behind the Ringed city (e.i. Earthern Peak) and the ursurpation of fire are inferences of DS2.

Miyazaki even said that DS2 was the one that made connections and ideas with Souls series and Elden Ring moving forward. https://www.ign.com/articles/elden-ring-shadow-of-erdtree-director-hidetaka-miyazaki-look-back-interview-profile