There is a patch for 1.9 that adds the functionality of changing settings to enable/disable emoticons, but it doesn’t quite work on 1.8. The best way to do it in Moodle 1.8 is going to your moodle directory, then lib/weblib.php and look for the function replace_smilies (line with “function replace_smilies(&$text)”) and comment them out until after the very last one, which would be the ‘( )’ => ‘egg’ entry.
The benefit of this is that during parsing of text emoticons will not get automatically added, although they can still be used if selected from the menu of an editor. A note is that you should keep at least one valid emoticon entry in the $emoticons array, just to make sure that it doesn’t break anything by making $emoticons empty.