Not sure what you mean, email signatures were standard well before Outlook. What changed is that the convention of beginning them with a line consisting of “-- ” wasn’t adopted by Outlook & friends, so automatic detection/hiding/non-quoting suffers.
I mean that we already have SMTP headers for metadata.
Such as in-reply-to (no need to quote the whole mail at the bottom of yours) and obviously the sender (no need for an explicit signature), and you could use x-face if you needed something fancier or, if your company really really needs to remind everyone how social they are at every message, you could have added an x-coprorate-blurb custom header, etc.
Whatever, emails these days are nothing more than an archaic last resort password reset protocol.
