Here is my code. If you go to "Plugin Manager" in your control panel, then find and Edit Plugin "Answer Forums - Show answered/notanswered In Forum" You can replace it with this and your own image links of course!
Code:
if($vbulletin->options['g_answer_forum_show_forumdisplay']){
// Set cutoff date if once is applied
$af_cutoff = $vbulletin->options['answers_forums_cutoff_date'];
if($foruminfo['g_answer_forum'] AND THIS_SCRIPT == 'forumdisplay' AND ($thread[dateline] > $af_cutoff OR $thread['g_answer_forum_answer'] != '0')){
if(!$thread['g_answer_forum_answer']){
$thread['movedprefix'] = '<img src="/forum/images/icons/exclamation.png" border="0" title="Not Answered">' . $thread['movedprefix'];
} else {
$thread['movedprefix'] = '<img src="/forum/images/icons/accept.png" border="0" title="Answered">' . $thread['movedprefix'];
}
}
}