Ask HN: How to verify a BlockSign transaction in the Bitcoin blockchain?

""A BlockSign Transaction is a transaction on the bitcoin blockchain representing legally binding signatures on any document, contract, or agreement. It can be any bitcoin transaction with at least one Pay-To-PubKey-Hash Input and at least one BlockSign Output.

The PubKey Hash (aka. Bitcoin Address) in the Pay-To-PubKey-Hash Input identifies the signer (or signers) while the hash digest embedded in the BlockSign Output identifies the document being signed.""

I can understand how a document can be signed and bound, but the process of verifying the signature is still obscure to me !

Can anyone clarify this please ?