A Credible identifying witness = human ID

A Credible Identifying Witness = A Human ID A credible witness may be used when a signer does not possess satisfactory evidence or acceptable identification and it would be difficult or impossible to obtain one.

One credible witness may be used to identify the signer if the witness personally knows the Notary and the signer. 

Two witnesses who do not personally know the Notary may be used as well. Just like signers, a credible witness cannot be identified based on the Notary's personal knowledge.

SIGNATURE BY MARK 

In the event a signer is unable to sign their name for any number of reasons, a "signature by mark, can be used in CA.  Two witnesses must observe the signer making the mark.   The client must appear before the notary in person. The client must be aware of their actions, and be properly identified according to state law.  The two witnesses must also sign the document. 

PROOF of EXECUTION BY SUBSCRIBING WITNESS 

This notarial certificate is used when a principal signer, who cannot appear before the Notary, directs a third party (the subscribing witness) to witness that principal's signing or acknowledging of his or her signature on a document.  

What is the difference between a credible witness & subscribing witness?
Notice that the credible witnesses only signs the journal and not the document whereas the subscribing witness must sign both.