Crossword Genius

Signs system recomposed anew with Papa dropped (5,4)

Ross

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" .)

I've seen this clue in The Independent.
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