It serves as a prompt on stage (3)

I believe the answer is:

cue

(Other definitions for cue that I've seen before include "Snooker player's stick" , "Billiard stick - hint - signal" , "Sports implement" , "Tapering stick used by snooker player" , "Prompting" .)

I've seen this clue in The Irish Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.