You Died Symbol Reference: Circle Shield Design
You Died features a symbol of a circle on page 351. This is a reference to a shield design found in Dark Souls: Design Works on page 106.
This design never made it into the final game as far as I know. Please get in touch on the Tune & Fairweather Discord if you know more.
It stands for the letter J in the decryption key for You Died and Abyssal Archive.