hazy also another issue, in addition to the bot thing, is that users should be able to verify the claim on their own. on Discord, you're creating a public invite anyone can view via the API, or simply use. same for Telegram. on Matrix, you're sending your proof to a public channel. on IRC you're assigning a public property to yourself using NickServ.
on Signal the closest thing would be one of the following:
- to have your username as a claim and have the proof in your profile (probably in the "about" field)
- to join a public group and send a message there
- create a public group with the proof as its name/description
all of which are problematic since Signal isn't designed with public groups or public profiles in mind, and as such the safety of the encryption is prioritised over protection from strangers contacting you.