As far as I've been told, carving is done with round or v-shaped carving tools. Ivory is carved out. A groove is made.

Schrimshaw is done with pointed tools. Scrimshaw is akin to scratching or making pointed holes, carving is done with strokes.

If you blow up a scan of a scrimshawed ivory chip, you will see raggedy edges from the scratching. A carved chip will show a smooth line, even when the scan is blown up.

My point is the antique ivory chips were carved. The skull and cross bones was scratched or scrimshaw. Some may call scrimshaw scrimshaw carving. There is, however, a big difference to carving and scrimshaw.

I have a scan somwhere (which I displayed on this board) comparing the two. The difference was quite apparent.