Legitimately would love this kind of thing integrated into my password manager (1password)Reply
I was thinking of integrating something like this into my spam filter. However it would probably be something slightly different. Add the "name" into the email as plaintext, this both makes it easy for me to find out where this email came and search for emails from the sender from but also allows this to be automatically verified.
Then the spam filter can check that `signature == hash(salt + "google")`. Anything that doesn't fit is marked as spam.
Of course most people don't have a flexible enough spam filter to do this.
You probably also want versioning for leaks. You can bump the version and change your email with the service.Reply