Comment by fullstop
And if you move across the country the local animal control / humane society may use different registries.
It's a great idea, in theory, but it's opened up a world where the possibility of scam registries can exist.
I've considered the challenges of an open and public registry, but allowing the public to access it is problematic as there is no way to validate the entries and you would be handling people's contact information. It might be an actual use of a distributed blockchain / public ledger.
Maybe there is no need for a centralized database of contact information, but there could be one for found pets.
Single resource. Any vet/shelter/guy with a RFID scanner can report found pet with this barcode at approximately this location. If you know this pet, contact us here. Presumably only vets and shelters would be adding to the database, so all of the contact information is already public. People who have lost their pets can then monitor this location/sign up for alerts after you lose Fluffy.
Not as great as being able to immediately lookup the owner, but eliminates some privacy concerns.