When the signer of an instrument cannot write (sign) their name, that person may sign the document by mark.(Civil Code section 14) The requirements for notarizing a signature by mark are as follows: The person signing the document by mark must be identified by the notary public by satisfactory evidence. (Civil Code section 1185) 
Must Be Witnessed
The signer’s mark must be witnessed by “two persons” who must subscribe their own names as witnesses on the document. One witness should write the person’s name next to the general information person’s mark and then the witness should sign his or her name as a witness. The witnesses are only verifying that they witnessed the individual make his or her mark on the document. 
A notary public is not required to identify the two persons who witnessed the signing by mark or to have the two witnesses sign the notary public’s journal. Exception: If the witnesses were acting in the capacity of credible witnesses in establishing the identity of the person signing by mark, then the witnesses’ signatures must be entered in the notary public’s journal.
Notary Journal
The signer by mark must include their mark in the notary public journal. To qualify as a signature, the making of the mark in the notary public journal, must be witnessed by an individual who must write the person’s name next to the mark and then sign their own name as a witness. 