What's with the annoying "Save" shit that appears everywhere?

[rado84]

At first I saw this crap while I was changing my signature and it took a few attempts to get rid of it. It's still in my signature but at least it's invisible now (thank he who doesn't exist). But now it appeared in my latest post. It's just a text, there's no function of that text. The strange thing is that it appears only on this forum.

It's even stranger because if you click on "full edit post", you can't see it in the post:


But if you click on "view source", it's there - the last 2 lines:


And I can't get rid of that thing. If I delete it, save the edited post and then return back to full edit and source view, it's back.