I found this on the FAQ page:

> Q: In my profile, what does showdead do?

> A: If you turn it on, you'll see all the stories and comments that have been killed by software, moderators, or user flags.

> If you see a [dead] post that shouldn't be dead, you can vouch for it—when enough users do this, the post is unkilled. Click on its timestamp to go to its page, then click 'vouch' at the top. There's a small karma threshold before vouch links appear.