If there was a spy who was a notary, what would he be like? Everything would have an alternate meaning. If he sent an Affidavit, all the words in it would be encoded. But, the person receiving the Affidavit would not understand it until they went and had it notarized. The notary would then answer or decode the message in the Affidavit, but adding a notary certificate to the document. But, the choice of certificate wording would be part of the code or decyphering mechanism. Or there could be wording in invisible ink in the Acknowledgment section that could be given to the document custodian.
This way, if other spies were watching what their subject was doing, they would have no idea that the notarized statement contained the secret information they were looking for. It would all look so innocent — until they caught on.