User blog comment:Kaido King of the Beasts/Chapter 908: Imminent, Imbalanced, Improbable Whims/@comment-49.191.8.180-20180616020448

And thus we meet Davy Jones, ruler of the world and ex-captain of Big Mom and Kaido.

I'm thinking the Shirahoshi and Vivi posters are related to their status as royalty (although that brings Blackbeard and Luffy into question). Alternatively, this is to do with the Ancient Weapons - I know people have pointed this out for Shirahoshi, but think people have forgotten about Alabasta's Pluton Poneglyph.