Quite simple really, Drop the star image and use a chat bubble in it's place for the "you've posted". Bare in mind, I'm tired so it seems like a good idea to me. (Mockup below) (updated with the icons floated to the far right)
AFAIK, the star currently only symbolizes whether or not there are new posts in the thread. So does the boldness of the thread title. It's a bit redundant to have two things convey the same thing. The whole idea is to stop using the star to symbolize new posts (and instead relying on the boldness of the thread title), and to use the speech bubble to signify whether or not you have posted in the thread.
As cool as it is web design-develop wise, I agree, don't show in a UX/UI what isn't needed, when it's not logical to display it. And show it, as the exception to the situation, so you draw attention to it.