Only the matching public key will authorize a macro signed with a private key.
Verifying your certificate is possible because the computer that you create the certificate on already contains some information about your digital certificate.
Behind every digital certificate is an encryption mechanism that uses keys: a public key and a private key. The private key is used when signing the macro; the public key is attached to the macro to verify the signature. Because only the writer of the macro has access to the private key, the fact that the signature can be verified with the public key indicates that the writer of the macro created the signature. This is true of all certificates, not just self-signed certificates.
How does that help you? If you use a macro carrying a public key on a computer that has the matching private key on it, the public key is recognized and the macro is not automatically disabled. You then get the option to add that certificate to your store of trusted publishers.