death's–head
: a human skull or a depiction of a human skull symbolizing death
http://www.merriam-webster.com/dictionary/dea...

Later that month, the printer of the Pennsylvania Journal replaced his newspaper’s masthead with a death’s-head and framed his front page with a thick black border in the shape of a gravestone.
http://www.newyorker.com/arts/critics/atlarge...

Gänzlich falsch scheint der Bindestrich nicht zu sein.

http://dictionary.oed.com/cgi/entry/50058239?...
death's-head
1. The head of Death figured as a skeleton; a human skull; a figure or representation of a skull, esp. as an emblem of mortality.
1596 SHAKES. Merch. V. I. ii. 55, I had rather to be married to a deaths head with a bone in his mouth. 1597 {emem} 2 Hen. IV, II. iv. 255 Doe not speake like a Deaths-head: doe not bid me remember mine end. 1684 Lond. Gaz. No. 1987/4 Several Jewels and Rings, one of which was Enamelled with a Deaths-head. 1768-74 TUCKER Lt. Nat. (1852) II. 659 Hermits and holy men are described sighing over death's heads, sobbing and groaning at their being men and not angels. 1822 SCOTT Pirate xl, The old black flag, with the death's head and hour-glass. 1864 THACKERAY D. Duval ii, His appearance..was as cheerful as a death's head at a feast.
fig. 1641 MAY Old Couple III. ii. (1810), As the two old death's-heads to-morrow morning Are to be join'd together.

http://encarta.msn.com/encnet/features/dictio...
death's head (plural death's heads)
noun
Definition:
human skull or its image: a human skull or its representation in art, often a symbol of mortality

Der OED fuehrt noch den Bindestrich, wenn er auch in den Beispielen oft fehlt. Wie bei vielen anderen Woertern, ist die Bindestrich-Schreibweise die (meines Wissens nach) etwas aeltere. (Vgl. death-bed und deathbed)

Ich wuerde daher die Bindestrich-freie Schreibweise nachtragen, ohne die existierende zu loeschen.

Vielleicht liegt das Überleben des Bindestrichs nur daran, daß man den Begriff wegen des Apostrophs nicht zusammenschreiben kann. LEO kennt weitere Beispiele:

Dictionary: *'s-*
adder's-tongue
bird's-foot
crow's-feet
...

This should actually be in as "skull and crossbones" which is WAY more common

UKer, das ist doch gar nicht das Thema hier. "Skull and crossbones" ist schon lange in LEO: Dictionary: Totenkopf