A warm welcome to Rootschat, monkhouse.
This site is quite interesting:-
http://www.graveaddiction.com/symbol.htmlAs Ruskie says a skull and crossbones is a symbol meaning mortality & death.
There is a headstone in the graveyard of St Marys, Newchurch in Pendle with such a symbol on it. As it is a Nutter family grave, people mistakenly assume that it is the grave of Alice Nutter, one of the supposed Pendle witches. This cannot be the case as a convicted witch would not have been buried in consecrated ground.