
Although I am certainly no expert on Jewish tombstone symbols, I must comment on the caption in the Jamaica cemetery section of this blog which implies that the skull and crossbones are symbols for a Jewish pirate's grave.
I recently was lucky enough to visit the site of the oldest Jewish cemetery in England in the grounds of Queen Mary's College, Mile End in the East End of London. Here are some photographs I took on my visit.
It is now hemmed in by buildings on two sides and has little to show of its former status as the graves were horizontal and are mostly now completely covered by turf and unreadable (left below).
There are a few other remains stacked by the perimeter wall, all having skull and crossbones on them (see below). The cemetery still has a very special feel and is very peaceful - a haven in the bustling and rather delapidated Mile End.The Old Velho Sephardi Cemetery, as it is known, was created just over 350 years ago on the orders of the Lord Protector, Oliver Cromwell, who, overruling his own council, officially readmitted Jews to England for the first time since their expulsion in 1290. It was opened in 1657 and closed in 1742. It was the first Jewish cemetery to be opened following the readmission of Jews to this country under Oliver Cromwell.
A particular feature of Sephardi cemeteries are the flat tombstones which I am told symbolize that all are equal in death - rich or poor, high or low. Abraham Fernandez Carvajal, the founder of the modern Anglo-Jewish community, is buried in the old Velho cemetery as as well as Haham David Nieto, one of the greatest Sephardic spiritual leaders (born Venice 1654 - died London, January 10, 1728) and the physician Dr. Fernando Mendes. This interesting article discusses the background of Carvajal and the early Sephardim in London; read here about David Nieto. Above right, see an image of the decaying wall plaque listing leaders of the community.
Surely the skull and cross bones in a universal symbol for death and fleeting nature of life and has nothing to do with pirates who could not have lived and flourished in Mile End in the 1600s?

These symbols from an early Scottish Christian cemetery look very similar to the ones in the old Velho cemetery: