This can be as simple as including a textfile as an attachment to your post, or just copy-pasting the license text, or even including a pic like this:
Otherwise, projects that try to respect rights and licensing can't really use them comfortably, especially when you're not around to say "Yeah, i gave permission."
I'd suggest CC-0, since the Creative Commons licenses are pretty much universal for art and music, and the other CC licenses impose a variety of restrictions on how the work can be used.
It's the art equivalent of the permissive free-and-open-source licenses like MIT and freeBSD.
Global Forum Rules have been updated for clarity of this matter. Send a PM to Forum Admins if you have any concerns about this.
Creative Common's website lists their attributed licenses and public domain licenses. See their License Chooser if you're not sure what to pick.Global Forum Rules wrote:Asset Licensing
Unless otherwise stated, it will be assumed any user-made assets (i.e. maps, sprites) posted here has an implicit license of Creative Commons Attribution-ShareAlike 4.0 International License. If you want your assets to be licensed differently then you must attach a license to your post;