Cameos are low-relief usually portraits that are most commonly carved out of conch seashells. So in this respect bein a low relief carving Lincoln's head or any head for that matter carved on a penny is a cameo.
Cameos are typically worn as jewelry in the form of a pendant, brooch, centre of a bracelet or the a ring. It is a very old form of art and dates back to the 500 A.D maybe even earlier.
To create a sculpture in relief is to give the impression that the sculpted material has been raised above the background plane. What is actually performed when a relief is cut in from a flat surface of stone (relief sculpture) or wood (relief carving) is a lowering of the field, leaving the unsculpted parts seemingly raised.
The technique involves considerable chiselling away of the background, which is a time-consuming exercise with little artistic effect if the lowered background is left plain, as is often the case. On the other hand, a relief saves forming the rear of a subject, and is less fragile and more securely fixed than a sculpture in the round, especially one of a standing figure where the ankles are a potential weak point, especially in stone. In other materials such as metal, clay, plaster stucco, ceramics or papier-mache the form can be just added to or raised up from the background, and monumental bronze reliefs are made by casting.
There are different degrees of relief depending on the degree of projection of the sculpted form from the field. High relief (alto-rilievo) is where more than 50% of the depth is shown and there may be undercut areas, mid-relief (mezzo-rilievo), low-relief (basso-rilievo, or French: bas-relief), and shallow-relief or rilievo schiacciato, where the plane is scarcely more than scratched in order to remove background material.
There are some famous cameo carvers names at the fllowing links but no actual photo of the mark to cross reference.
Your cameo looks quite modern and in very good condition. A very beautiful cameo and thank you for sharing.
