There are a number of official documents that require a notarized signature.  Only a Notary can perform this service.  The Notary witnesses your signature and verifies that s/he confirmed your identity and that you were the person who signed the document.  One of the most common times individuals encounter notaries is during a closing on a house.  Home mortgage closings feature a number of legal documents which must be signed and, and those signatures must be witnessed.  A Notary Public can witness and certify the signatures on these important documents.