Copper gets point of signal (3)
I believe the answer is:
cue
'signal' is the definition.
(as in an actor's cue)
'copper gets point' is the wordplay.
'copper' becomes 'Cu' (Cu is the chemical symbol for copper).
'gets' is a charade indicator (letters next to each other).
'point' becomes 'e' (compass point).
'cu'+'e'='CUE'
'of' is the link.
(Other definitions for cue that I've seen before include "Prompt; signal" , "Rod used in billiards" , "On a car[D?] this would give a prompt" , "Actor's prompt" , "Actor's words" .)