Comment 32 for bug 303140

I must be a complete noob.
Please explain:
1. Where exactly the following is, or what steps need to be followed: "click in the header pane to the left of the attachment list box. When I did so, an interesting thing happened. The icon for a signed email appeared there"
2. Tried to help myself by finding the bug report duanedesign mentioned, but can't find a url for: Bugzilla#453490