Docusign could put a stop to a good chunk of these but they choose not to. They know attackers are abusing their free trial service to send these out using docusign's own domains. Just gate the trial behind a sign-up/sales call.
I sometimes enjoy reading through my spam folder. I get a lot of docusign phishing (despite not being an important executive). I also get a lot of "docusing" phishing, which gives me a chuckle. Is it bardic spam?