Walk-on part arrived with Oscar (5)
I believe the answer is:
cameo
(Other definitions for cameo that I've seen before include "Small role - gem with a figure carved in relief" , "Item of jewellery with a portrait - distinguished actor's minor role" , "Piece of jewellery with carved portrait" , "Small piece of carved stone or small role in play" , "Something small but well done - say role in play" .)