I don't think it's a message to the moderator at all - just a way of forcing it to actually happen. Most recently replied to threads are always at the top so if a post falls off the first page, you can return it to the top of the list by replying to it. A "bump" is just replying without actually saying anything. It's only purpose is really to get the thread back to the top.
If you want the thread to remain at the top you can ask a moderator to "sticky" it and that is completely their discretion as to whether they do so.
If you promise not to bump it, you can view the Shana thread
here .