In the forum software used here, a pair of brackets is used as the holders for any markup. You can see this effect by highlighting some text and clicking on one of the formatting icons, and you can see the specific markup for a particular effect just moving your cursor over an icon and watching for the explanatory popup text. Parentheses are not used for this purpose, so are regarded as safe when posting asides or other parenthetical thoughts on a forum.
The markup language used on this (and most other) forums is essentially a simplified version of HTML, with the additional difference that the markup language is offset with brackets in markup but with angle brackets (i.e.: "<" and ">") in HTML.