Carved pictorial gem (5)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
cameo
(Other definitions for cameo that I've seen before include "Brief role" , "Small role for a well-known actor" , "Medallion with a profile carved in relief" , "Small part for star actor" , "Carving in relief, on a brooch say" .)