User blog comment:Kaido King of the Beasts/Three Things You Never Forget: 9.11, Harambe, and the Debt I Owe You/@comment-27930128-20160916134034/@comment-3507581-20160919041319

Like 12th Supernova said, it is a tribute to Kochikame (or Kochira Katsushika-ku kameari koen-mae Hashutsujo), which ended after 40 years of serialization and 200 volumes (it even became the recipient of a Guinness World Record for the Manga series with the highest number of volumes). It even got the cover in this week's issue -which is rare for a closing series in Jump-, and in it and in the opening color pages several Jump artists tributed its protagonist drawing him in their own styles.

Said character is in the wanted poster; he's Kankichi Ryotsu (affectionately called Ryo-san), the main character, and the character Luffy wrote is in fact the well-known shape of Ryotsu's eyebrows.