The interesting aspect of the stamp is that there is an additional image only visible under ultraviolet light.
I tried to get a decent picture of it under UV light - it was a little bit clearer to the naked eye, but the camera didn't get a great shot. It looks like a reddish person (a medieval knight, maybe?) holding a pennant.
Update: definitely not the knight idea - it is the classic cowled figure of death, scythe in hand. Thanks for the correction from Eva.
A cool idea, and I love the gorilla (King Kong, I assume) on the stamp. It accompanied this great card, which I appreciate being a fan of science fiction.
Enjoy more links to U-themed stamps over at Sunday Stamps.