SO is it CC0 (public domain)?
If yes, you should add the license into metadata for the asset packs:
"Edit asset pack->Metadata->Release Info->License for assets" It will increase the size of audience that will be able to find your art
If you think that it was useful for you, you can leave a comment here to support my proposal about making metadata more visible for those who are interested in it https://itch.io/t/2919128/metadata-encouragement#post-7952450