Primatoide Futile brings us these engraved protective tokens bearing various Lovecraftian sigils. She does a nice job of recreating the look of stone using Super Sculpey.
If you're ever tempted to try something like this with real rocks, like the polished river stones available at craft stores, I would suggest going very low tech. It can be done with a Dremel, but you'll go through bits like crazy. It's actually easier to use a nail mounted in an X-Acto handle to patiently scribe the figure into the stone.