The new version of Mastodon server has an optional admin feature where referrers can be sent when people click links. Enable it for large servers.
Here’s it in action - when people on my Mastodon server click links to my blog, I can see they’re from Mastodon. Other publishers can too. It will drive the importance of Mastodon as a platform. Almost all my traffic is under “direct”, which I strongly suspect is Mastodon servers without the feature enabled.