Some forum posts have diamonds - mIRC Discussion Forums

Indeed you will find changes like these in quite a few posts. They have occurred several times since the forums were created, usually whenever the forum software was updated and posts needed to be re-parsed. It is probably due to conversion between Unicode and a particular codepage. Unfortunately, it is almost impossible to spot issues like this until long after the update has been performed, due to the large number of posts, and they are not reversible.