Meta tags in forums are dynamically created using the forum name and description... but you need to have the f=XXX in the url, otherwise the META TAG is not generated (I've coded this in this way to avoid further SQL while browsing topics).
Try to look at the page_header.php and you'll se how the code is working... especially this part:
elseif ( isset($meta_forum_id) )
{
$sql = "SELECT c.cat_title, f.forum_name
FROM " . FORUMS_TABLE . " f, " . CATEGORIES_TABLE . " c
WHERE c.cat_id = f.cat_id
AND f.forum_id = $meta_forum_id";
if( ($result = $db->sql_query($sql, false, 'forums_cats_')) )
{
if ( $meta_row = $db->sql_fetchrow($result) )
{
/*
$meta_description = $board_config['sitename'] . ' :: ' . $meta_row['cat_title'] . ' :: ' . $meta_row['forum_name'];
$meta_keywords = $board_config['sitename'] . ', ' . $meta_row['cat_title'] . ', ' . $meta_row['forum_name'] . ', ';
$page_title = $board_config['sitename'] . ' :: ' . $meta_row['cat_title'] . ' :: ' . $page_title;
*/
$meta_description = $meta_row['forum_name'];
$meta_keywords = $meta_row['cat_title'] . ', ' . $meta_row['forum_name'] . ', ';
$page_title = $meta_row['cat_title'] . ' :: ' . $page_title;
}
//here we clear $result from ram and cache it
$db->sql_freeresult($result);
//End sql cache opt
}
}