The QR code is just a convenience feature. If you look at the sticker you see a short alpha numeric code, that's what's on the QR Code.

You can type that alpha numeric code into the Certisfy app to verify the sticker: https://certisfy.com/app/

You'll probably never use a social security certificate directly, it will be used as a IRL "identity anchor" certificate as described here: https://cipheredtrust.com/doc/#pki-id-anchoring

Yes a fraudster will happily take a stolen card but it will be of no use to them if they try to use it via Stripe for instance to post a charge but Stripe requires a cryptographic signature for a certificate for the card :)

So sure the card processor has to require the signatures to make it effective. In other words the secrecy of the card number becomes irrelevant if it requires a certificate signature before it can be used, only the owner of the card has the private key on their device to generate the signature. Secrecy is still useful for privacy.