My initial idea what that sites could look up a combo of an email and sign to see if they are a match by Looking up the algo used to make it.
But I realized this wasn’t all that necessary once i realized you can include the hashing protocol in the code so sites that you have account for can verify on their own without third party.
I guess i forgot that there is no point left for the sites to be used to verify as all it really will tell you is that yes that is a valid sign registered here. But i see no reason why a competitor cant try the same thing.