It's not immediately possible and you'd need to do a couple of small PHP things.
First, in qa-db-selects.php, move the following line out of the if (...) it's within:
$selectspec['columns'][]='^posts.selchildid';
(This will be done in the next release of Q2A anyway.)
Second, create an advanced theme, and override the appropriate function, depending on where you want the icon. Perhaps post_meta_what() in which case your copy of the function should include the following code:
if (isset($post['raw']['selchildid'])) {
$this->output('HTML CODE TO DISPLAY YOUR ICON');
}