Signals copper on points (4)
I believe the answer is:
cues
'signals' is the definition.
(I've seen this in another clue)
'copper on points' is the wordplay.
'copper' becomes 'cu' (chemical symbol).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'points' becomes 'es' (two compass points).
'cu'+'es'='CUES'
(Other definitions for cues that I've seen before include "Prompts for action" , "Snooker ball strikers" , "Actor's signal" , "Snooker rods" , "Signals for action" .)