new thread sql querie

[rob01]

hello i was thinking in adding something, so when a Admin, moderator , replies to a thread a small image will appear besides the thread name, saying a moderator has added a new replay

i was thinking something like this:
(when the moderator post)
"UPDATE user SET GM='1' WHERE id='$userid'"

for cheking if the post should add a picture or not
$db->query_read("
SELECT GM
FROM " user "
");

i know is not complete, i will try to finish it tonight

but what you think about the idea?