When using Pleroma.Web.Metadata.Providers.RelMe and profile metadata has a[rel="me"] value, will be added link[rel="me"]. Users can make it verified their account from another accounts by verifiers such as Mastodon.
Note: Pleroma can write HTML to profile metadata values so users can make it verified on both accounts by input values like: <a rel="me" href="https://fedibird.com/@kPherox">https://fedibird.com/@kPherox</a>