Newsgroups with an extension that signed your post as a verified account (handled by whatever the moderators decide is good) and with some middleware to accept signed/allowed posts automatically would probably do it, if you could get people to actually use it enough to get momentum.
Edit: I suspect something like this probably existed. It seems straightforward and obvious enough that I'd bet it did exist, but couldn't get much usage in a world where spam wasn't quite as bad, numbers of users were smaller, and people were already shifting to HTML based platforms.
Edit: I suspect something like this probably existed. It seems straightforward and obvious enough that I'd bet it did exist, but couldn't get much usage in a world where spam wasn't quite as bad, numbers of users were smaller, and people were already shifting to HTML based platforms.