Look, I'm going to help you out.
Feeling generous and maybe this will squash this friggin' question once and for all!
You see that box up above, top left that says "my forum profile"?
Click that.
Now, down the left side click on "view public profile".
You see that?
..what does it say underneath your username? Noob or something, right?
Well, you need to keep posting until is says "Herf-a-holic".
When it says that underneath your username it will unlock a special link that you can only see there.
You then click that and you'll be taken to special membership sign-in.
Simple.