Just like you would write any other letter. It is not the significance of the letter that matters, it is the identity of the signer that the notarization focuses upon.Notaries Public authenticate the identity of those being notarized by examining some form of government issued, photo ID that proves this.For any letter to be useful, I would include name, address, date and purpose of the letter or statement, such as a title at the top of the letter. That will help anyone reading the document later, to have a clear understanding of your purpose.