I'd have found it helpful if the CAPTCHA thing told you when it came up that it was for the first 3 posts.

Forum rules usually have a lot of text and say much the same thing -since I'm not a troll/spammer I don't generally care what the details are and wouldn't remember them from forum to forum anyway. They're something I only bother to read if I'm considering a post that I think might be dodgy for some reason.

I did find the CAPTCHA thing annoying enough that I came looking to see what cookie or script I needed to enable to get rid of it.