Basically, I am working on creating a new version of the Flat overlays for 18.5:9 displays. I am currently housing them in my own GitHub repo until I get something usable and I will then submit a pull request. My question is really about licensing. There is no license/copying file in the libretro/common-overlays repo which is where I pulled these from. My assumption is that since the overlays are really just default configs that no license would apply here, but I wanted to confirm before I shared them with the world 
The configs may not be license-able, dunno, but the assets certainly can be. Unless otherwise stated, I would assume GPLv3, since they’re intended for use with RetroArch and that’s its license.
So just to be sure, since I know nothing about this, I should put the GPLv3 in my repo?