Egyptian symbol worn by Death in the award winning comic book series by Neil Gaiman, Sandman.
Interpretations of the ankh vary; the simplest definition being life. Some also believe that it represented balance - specifically the balance between life and death, though also the balance of man and woman.
The key to it all was that you could not have life without the existance of death - the two hold each other in check.
As for why Mike Dringenberg, the artist who developed the image of Death for Gaiman and Sandman, chose the ankh in his visual interpretation of Death:

"Part of that simply came out of the ankh being in vogue at the time. I also like the irony, though, because the ankh is the Egyptian symbol for life; and in some other cultures it became a symbol for immortality."
-- taken from The Sandman Companion, by Hy Bender. Copyright 1999.