Well all you have to do is to look at the function in SSI.php. Scroll down until you see what is in the array that it is creating.
You can see what is available when the function is called.
// Build the array.
$posts[] = array(
'board' => array(
'id' => $row['id_board'],
'name' => $row['board_name'],
'href' => $scripturl . '?board=' . $row['id_board'] . '.0',
'link' => '<a href="' . $scripturl . '?board=' . $row['id_board'] . '.0">' . $row['board_name'] . '</a>'
),
'topic' => $row['id_topic'],
'poster' => array(
'id' => $row['id_member'],
'name' => $row['poster_name'],
'href' => empty($row['id_member']) ? '' : $scripturl . '?action=profile;u=' . $row['id_member'],
'link' => empty($row['id_member']) ? $row['poster_name'] : '<a href="' . $scripturl . '?action=profile;u=' . $row['id_member'] . '">' . $row['poster_name'] . '</a>'
),
'subject' => $row['subject'],
'replies' => $row['num_replies'],
'views' => $row['num_views'],
'short_subject' => shorten_subject($row['subject'], 25),
'preview' => $row['body'],
'time' => timeformat($row['poster_time']),
'timestamp' => forum_time(true, $row['poster_time']),
'href' => $scripturl . '?topic=' . $row['id_topic'] . '.msg' . $row['id_msg'] . ';topicseen#new',
'link' => '<a href="' . $scripturl . '?topic=' . $row['id_topic'] . '.msg' . $row['id_msg'] . '#new" rel="nofollow">' . $row['subject'] . '</a>',
// Retained for compatibility - is technically incorrect!
'new' => !empty($row['is_read']),
'is_new' => empty($row['is_read']),
'new_from' => $row['new_from'],
'icon' => '<img src="' . $settings[$icon_sources[$row['icon']]] . '/post/' . $row['icon'] . '.gif" align="middle" alt="' . $row['icon'] . '" />',
);