wow, the forum stole the underscores in the filename o_O
A feature of Markdown, which is used on this forum. The underscores are for emphasis—why the emphasis does not display on the forum when underscores are used, I don't know. In any case, I edited your comment slightly and escaped them for you.
P.S. As a side note, Markdown allows you to use HTML tags directly. So if you want/need emphasis you can still do it via the <i> tag. We filter out many HTML tags to prevent craziness but these are allowed through.