Mastodon has a concept called "pinned statuses", which is a special collection attached to a Person actor.

docs.joinmastodon.org/spec/act…

It wasn't readily known how this collection is updated and federated (not without code achaeology), but claire@social.sitedethib.com recently shared some additional info :smiley:

• The actor itself will issue an Add activity targeting the collection with the status in object.
• This activity is sent to all followers of the actor.
• No activity is sent if the actor has no remote followers.
• A Remove is sent when a pinned post is unpinned.

This is what the Add looks like:

{
    "@context": "https://www.w3.org/ns/activitystreams",
    "type": "Add",
    "actor": "https://example.org/users/testUser",
    "target": "https://example.org/users/testUser/collections/featured",
    "object": "https://example.org/users/testUser/statuses/115266412340579560"
}