Perhaps an extensible version of the Twitter blue checkmark scheme?
A trusted central authority (Jack) sets up a parameterised system that allows signing keys to be produced whose verification keys match identifiers. A Twitter service user (Lil Nas) sets up an account with Jack. Jack carefully verifies that Lil Nas is whom they claim (or simply allows them to select an unused identifier) and issues them with the signing key that matches their identifier. In addition to signing all of their transactions on Twitter so that anyone can verify the connection between the identifier and tweets, Lil Nas could also use the key to sign and validate transactions on other platforms such as TikTok or Instagram or DMs, uniquely tying the content to the owner of the account on Twitter.
Users only need the system parameters from Jack and a single signature verification to tie content to identifier, which is probably more lightweight and robust than PKI certificate-based solutions.