We need to state clearly
for example, all content is owned by the user and has a CC-by license...
There is some discussion on this topic at https://meta.discourse.org/t/who-owns-the-content-you-post-on-a-forum-aka-user-content-licensing/4261/14
For example, if you look at the main discourse site, the footer claims :
Content is by-nc-sa, Discourse logo and “Discourse Forum” ®, Civilized Discourse Construction Kit, Inc.
We could add this as a footer...
I have indeed added this as a footer, and included it in the site policies.