A long time ago, people left their mark in wax using intaglio carvings, which are carvings that are the reverse of what you wanted to see, pressed in wax dripped by candle. The primary use was to seal letters, but we cannot rule out that they might also have used them to make candies and little fancy butter pats with them.
Typically, they would be carved from carnelian or sard stone (as in sardonyx) and set in a ring. Carnelian is about my 14th favorite mineral I think. I bought these carnelian stones recently from a place in Colorado fancifully named 'The Gypsum Rose'. They were originally found in Madagascar, which sources some of the best exotic specimens these days. In order for you to have a really good and easily familiar frame of reference for how large the stones are, I included a perfect silver denarius of Alexander the Great with a seated victory in the picture.
The woman image at the top is an intaglio from the first century identified as Augustus Caesar's sister Octavia from the Luigi Cesnola collection provenance. It's weird to think that a family member or she herself might have stamp-sealed scrolls with this very object, or used it as a very small id badge for work or something.
I really want to buy a few tiny diamond bits and give intaglio carving into carnelian a try, but I have to come up with some good subject matter, maybe like the image below? I blame suggested YouTube cartoon watching mostly. I've read that ancient carvers would typically make a normal relief image, then cast that into a hard material, then fit it against the stone when carving to see where material still needed to be removed. That sounds a bit easier than just 'thinking backwards' when carving...
The Getty museum in California has a great exhibit going until September on gems and intaglio carvings by such great artists as Epimenes, Solon and Gnaios. And who can forget Dioskourides? The Getty article covers some information on the counterfeiting of these objects in the 18th and early 19th centuries. Anybody going?
There are quite a few intaglios on Ebay in various qualities, but hardly any of them are authentic antiquities, so as always, please be careful when shopping for old stuff. Particularly careful if the item in question has a Warner Brothers character carved in.
Voglio ritagliarsi storico firma anelli. Ho potuto acquistare uno, ma tutti vignette. Pertanto, lo so che non antiche. ;)