Requested feature overview description.
Introduce a metatag to enable searching for posts where at least one artist tag is verified.
Why would it be useful?
Verified artists' posts are generally pretty trivial to approve as a janitor, since they themselves are a valid source for everything attached to their artist tag, and DNP artists naturally have permission to post their own stuff.
Users might also be interested in discovering artists who are specifically proven to use e621 themselves.
What part(s) of the site page(s) are affected?
Search functions at /posts.

I also asked for this.

I guess two or more checkmarks would show up if there are multiple artist tags linked to the same user ID, but it would not be useful to search for that. True/false is fine.

Verification is dependent on an account link existing between the uploader and artist tag. It is strictly impossible for two artists to be verified on the same post at once. If the site code changes to allow that, then maybe there's a case for :some and :all, but until then? Nah.

bitWolfy has said "I doubt that it'll be implemented ", though without giving a reason. I don't know if it's some kind of privacy concern, or if the backend would have difficulty matching the necessary data in a search (it's one thing to check and display it when viewing a post, but going through to match each post's uploader that's also tagged with the same linked might put much more strain on the database, depending on how it's set up).