Every pope has the equivalent of a chief of staff, called the camerlengo. When a pope dies, the camerlengo must first certify that he is indeed dead. The ritual tradition is to strike him on the forehead with a silver hammer, calling his baptismal name three times. An alternative is to place a cloth over his mouth. If he does not respond, the camerlengo declares him dead, authorizes a death certificate and then seals the papal living and working apartments.
Later, the silver hammer will be used to scratch and break the papal ring and seal, so no documents can be forged in his name.
http://www.ucg.org/wnp/wnp0409/manpope.htmThey say the silver hammer was last used at the time of the death of Pius XII (before John XXIII) but no one really knows for sure.
Lennon/McCartney knew all about it:
Bang! Bang! Maxwell's silver hammer
came down upon her head
Bang! Bang! Maxwell's silver hammer
made sure that she was dead