Lined up as told, given signal (4)
I believe the answer is:
cued
'given signal' is the definition.
(to be cued is to be given a signal or prompt)
'lined up as told' is the wordplay.
'lined up' becomes 'queued' ('queue' can be a synonym of 'line up').
'as told' shows a homophone (sound like).
'queued' sounds like 'CUED'.
(Other definitions for cued that I've seen before include "Reminded" , "Gave prompt to forgetful actor" , "given a line" , "Prompted" .)