Well, I can tell you a few. Anchors were for hope. Poppies represented sleep and remembrance. Angels were associated with heaven. The thistle, now, it was a symbol of national origin.
Many Scottish people have a thistle carved on their headstone.
The carving techniques have changed or been lost. My ancestor, Robert, he did everything by hand, cutting all the stone and the lettering for the inscription. The monuments reflect a high level of craftsmanship. It could never be replaced. The monuments reflect social attitudes to death and fashions in funerary ornamentation since 1867.