Create a site where fake news (and its source) is mentioned, so it can be easier to check things up.
Then companies can check this website so that social media can tag things as "fake" (or simply remove them).
Realizing the Idea
It is needed that a reliable government/authority creates this site and updates it.
It might be funded with governmental means, for example EU.
It will be easier for users and social media to avoid fake news.
The idea is not particularly unique, but it needs governmental push in order to be implemented.