There are well-established guidelines for how the signature and date sections should look on a legal document. A party (or parties) should find credible, reliable witnesses to authenticate the signatures and date. Who can I have witness my legal document?
"Uninterested Objective Party"
Legal documents can be statements by one party (affidavits) or more complicated agreements between two parties (contracts). They can also be private or public. The ideal legal document would have each page time-stamped with the signature and date of both parties; but most agreements have plenty of pages in-between the first and last page.
Witnesses have two primary purposes: 1) authentication and 2) arbitration. The witness must verify that the signer of the legal document is not an imposter. The witness should be an adult of sound mind and not under the influence of any drugs. The ideal witness has known the signers of the document for a long time and does not have any financial interests in said agreement.
This third-party witness should keep a copy of the legal document for his personal records. If at some future time, the parties should display two different documents, then the neutral third-party can act as the arbitrator of such a dispute. Each party has his own interests to protect and cannot be objective. The neutral disinterested third-party can identify which legal agreement is authentic.
An example of someone who is not disinterested would be the beneficiary of a will. A beneficiary would have a financial interest in said will and would not be a good witness to the signing of said will.
"Notary Public Bank Agent or Judge"
The notary public is given authority by the government to be an official witness for signing legal documents. He or she will understand the required documentation, identification and procedures for official legal documents. The notary public has a stamp with its own signature space and date. His signature makes the document public.
You can also get a bank officer to guarantee your legal document. This is actually like security where the bank would be liable if fraud were involved. If you have been a long time customer in good-standing, you can ask a bank officer to be a witness.
Finally, a government official or judge could be a witness. Read the fine print on official documents; the government might want you to sign and date the document in their presence.