When a signer for whatever reason cannot write a signature, he or she may sign by mark. The customary mark is an 'X,' but other marks, such as a thumbprint, also are acceptable. To be regarded as a signature under law, the mark must be witnessed by two people.
Each witness should have no financial or beneficial interest in the document and actually must see the principal signer or "marker" make the mark on the document. An ideal witness must demonstrate honesty, awareness and impartiality. Generally, state laws allow a signer's relative to serve as a witness, but it's best to find someone else if the relative stands to gain or lose from the transaction in order to avoid an appearance of a conflict of interest.
You need not personally know the two witnesses, nor is it necessary for the witnesses to personally know the signer. Regardless of the circumstances, both witnesses should provide satisfactory evidence of identity.
The signature-by-mark witnesses must sign the document near the principal's mark, and one witness also prints the signer's name next to the mark. The same procedure is followed for the journal signature: The principal signs with a mark, the two witnesses also sign, and one witness writes the marker's name near the mark.
The signature-by-mark witnesses' addresses should be recorded in the additional information column of your notarial record if space allows. Otherwise, additional entry lines may be used.