Signs system recomposed anew with Papa dropped (5,4)
I believe the answer is:
morse code
'signs system' is the definition.
(communication system)
I cannot understand how the rest of the clue works.
(Other definitions for morse code that I've seen before include "Means of signalling by dots and dashes" , "Signalling language" , "Dot-dash alphabet" , "Dot-dash signalling" , "Way of signalling" .)