Gorousei's emblem

[GiantAlienHamster]

The emblem has actually been shown quiet clearly in the anime allready:

The thing in the middle is a lilly, which is a symbol for the holy trinity as well as a symbol for royalty

 

[blamagenkind]

http://www.mangareader.net/103-2577-1/one-piece/chapter-470.html
http://www.mangareader.net/103-2579-1/one-piece/chapter-472.html

I dont think the symbol at mareijoa has anything to do with devil fruits, since oda mentioned that whenever anything has to relate to DF it should have some spiral pattern.. which the symbol does not have

I think the three people from the left side of ch.472 are from Skypiea, look the their heads.
Also, I don't think the symbol is really significant, it doesn't feel right that there are too many of them. Maybe it's just an architectural design. But if it does have significance, I'm guessing it's a symbol for the three superpower countries from 800 years ago, the Ancient Kingdom, the World Government and another one(could be the fishmen race). Or the kingdoms from sky, earth and sea.

Edit: or it's just for royalty like GiantAlienHamster said.

 

[Lord Rayleigh]

The thing in the middle is a lilly, which is a symbol for the holy trinity as well as a symbol for royalty

Thanks for the picture but it's not a lily, it is a Fleur-de-lys. Lily is the english translation of the french word lys which is a flower. Anyway, the word Lys in Fleur-de-lys does not refer to the flower lys : it refers to the river Lys.

So the Fleur de Lys is a flower from Lys and not the flower lys itself. The real flower from the fleur-de-lys is an iris which grew in abundance all around Lys'riverbanks. That's the true origin of the French monarchy symbol.

 

[Geez]

I think the three people from the left side of ch.472 are from Skypiea

There's an article about this matter here