Yo! My mind is going into trance right now. All sort of theories are just jumping inside. Before understanding one, another theory shines in the dark corner of my brain. Let's see if my fingers can catch up with the spree. The following contains major spoilers following One Piece Chapter 818 Inside The Whale, read at your own risk.
Now that sensei [Oda] decided to give more insight about the four red [road] ponyglyphs, I just wanted to explore the potential places where it is located. Let's get started: