> Remember when email sigs were limited to 4 lines and had to have the double hyphen and a space on a line above?
I do not - sounds like a specific email client's thing rather than something in any IETF RFC.
It's from the pre-web internet of usenet, smtp and uucp in the 1980s.
Back in the deep dark past of bang email addresses and HOSTS.TXT when all Australian email addresses had !munnari at the end and everyone knew about !decvax and how to connect to it.