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A notary public is a public officer who bears witness to the signing of official documents. The notary seal assures all parties involved that the document is legitimate. The notary public must go through training and an application process through the state government. Notary publics can work just about anywhere, from a bank to a check cashing store to an insurance office, and must follow certain rules when witnessing the signing of documents.

Valid Identification From Signer

A notary public must view current, valid, government-issued identification with a recent picture from each signer before notarizing the document. The notary public must verify that each person signing the document is who he claims to be. Otherwise anyone could misrepresent himself by claiming to be someone else on a form and agree to terms of an agreement or make a statement on that person's behalf. The notary's reputation and status is at stake if she allows someone to sign without seeing valid identification.

Signature in Notary's Presence

The signer must place his signature on the document in the presence of the notary. So even if the person signed the document before he arrived at the notary public's office, he has to sign it again in her presence. The notary will check the signature against the identification to make sure they match. The notary has to be sure that the person is of sound mind (not under the influence of drugs or alcohol, or otherwise mentally unaware) when he puts his pen to the page.

Valid Official Seal

The notary public is assigned an official notary number per a "Certificate of Authorization" or similar document from the state government. The notary must then order a stamp embosser tool that will make an imprint in a piece of paper. The seal contains the notary's identification or commission number, county, city, state, and expiration date. The seal must be valid as of the date the notary public notarizes a document--an expired seal on a document invalidates the notarization.