Other moderator options
From Online Manual
In addition to the functions discussed on other pages in this category, moderators also have access to the following options:
You will find this button at the bottom of a topic. Clicking it will lock the chosen topic, which prevents any users who are not moderators or administrators from replying or modifying the topic's posts.
Set Topic Sticky
You will find this button at the bottom of a topic. There is also a Sticky this topic check box in the Attachments Additional Options (Additional Options in 1.1) section when you make a post.