Many states do not address or provide specific instructions to commissioned notaries on the proper way to notarize a signer who is blind. In any case, the requirements vary from one state to another and it is imperative the notary completely understand his/her obligations when notarizing the signature of a blind person.
The same is true for a signer who is disabled and unable to sign his/her name. Some states require the signer make at least a mark in their own handwriting. Other states, such as Oregon have provisions which allow a disabled signer to use a stamp or mechanical device to sign his/her name. In these instances, much like notarizing the signature of a blind signer the state may require witnesses be present.
The notary must not assist the signer. Guiding the hand of the document signer could appear to be an act of official misconduct. If the signer is blind the notary may want to use a signature guide card which is usually available through a visually impaired group or association. It is about the size of a business card and has the bottom third open to expose the document signature area which creates a small lip around the space for the signature the signer can feel with their pen to help them stay in the space without assistance.
In some states, if the document signer is unable to sign or make a mark due to a physical disability, the notary laws allow the signer to ask the notary to sign his/her name on the document being notarized only if done so in the presence of at least one impartial witness who has no legal or equitable interest in the transaction. The point is, the notary needs to consult with their state's regulations to determine how many witnesses will be needed and whether the person or persons sign the document or just the notary's journal.
Lastly, the commissioned notary must be sure they have fully researched the specific circumstances to ensure the act is executed properly including the form of acknowledgment or jurat being used for the specific circumstances.