[yokem55]

It could probably be done with a merkle based signature log that whoever is hosting the service could provide.

To cheat, the party hosting it would probably have to forge signatures for everyone after the disputed signature.

[yencabulator]

As long as we're talking about non-cryptographic-signatures, the party hosting the e-signing software can claim any signature to have happened at any time. The whole point was DocuSign would be unlikely to do this.