If a notary is asked to witness a signature, the notary simply observes an individual signing a specified document, according to the American Society of Notaries. Documents that can be witnessed by a notary do not require an oath or affirmation.
For a notary to witness a signature, the document signer must appear before the notary and present the document to be signed, explains the American Society of Notaries. The notary positively identifies the document signer through recognition of the signer or examination of identification documents. Then, the notary observes the signing of the document and completes the required notarial certificate, which usually includes a stamp and the notary's signature.