You Died features a symbol of two joined snakes. It’s a reference to concept art found in Dark Souls: Design Works, page 106. This design was used in the game on the Caduceus Round Shield.
The symbol of two joined snakes is featured in You Died: The Dark Souls Companion on pages 73, 115, 191, 192, 201, 229, 259, 263, 274 and 303.
It is also part of the symbol substitution table used to encrypt secret messages in the endpapers where it stands for the letter T and an easter egg featuring in an altered image in Soul Arts.