Some of Nash's stones are embellished with strange symbols:
If I had to guess, I would venture that Nash was attempting to copy the much more intricate stones of the Boston carvers of the late 17th century. Their stones occasionally have rows of cryptic symbols just under the death's head:
Mary Goose, d. 1690
Granary Burying Ground, Boston, MA
Richard Kettell, d. 1680
Phipps St. Cemetery, Charlestown, MA
If that's true, I would guess that Nash may have lived near Boston at one time and remembered that style after he moved west. Those symbols are uncommon on Boston-area stones carved after 1700, but Nash was carving them on his family's stones in the 1720s. This may be an example of an old-fashioned style surviving in a rural area after it has fallen out of fashion in Boston.