Yall way overthinking stuff.
Just give newbies and whatnot the checkbox option on their account which uses a predefined advertising space for this specific advertisement (the discord server); when you check the box, it just sets the text in the signature in the database. When you uncheck the box, it clears the text. No way to abuse the system.
Also; I forgot about 420. Yeah, that should get custom text.
For example, it used to say “Leet” when you hit 1337 posts.
Wait, they changed this? Lame. That's like one of the actual Easter eggs about the forum. I mean, given the sheer amount of threads created in meta about it over the years, I could see it being removed just due to this.
You removing your posts seems like your inefficiency. Should have combined them with edits instead. Even more so when others quote you