Not for the faint-hearted, but if you can figure out how to read/use the BBCode view of your post/reply, you can highlight parts of the text in order to emphasise them.

To do it, change the view of your post screen from Preview to BBCode and add the following code before the text to be highlighted (using copy/paste)...

and the following code after the text to be highlighted.

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Change back to the Preview view to see that it has worked and then post.