Where is that required? Maybe POAs? At least Florida and Georgia real estate law (the only ones I'm familiar with) don't require anything of the sort for any of the paperwork (before closing).
Of course, I also used https:/.opentimestamps.org to store the hash of our contract on bitcoin's block chain, because that way we both had proof that the contract existed in a certain form on that date. (I never needed that proof, because he was a good landlord, and I paid rent on time.)