Bookkeeper's sign represented rain (9)
I believe the answer is:
librarian
'bookkeeper's' is the definition.
(thesaurus)
'sign represented rain' is the wordplay.
'sign' becomes 'libra' (sign of the zodiac).
'represented' indicates an anagram.
'rain' is an anagram of 'rian'.
'libra'+'rian'='LIBRARIAN'
(Other definitions for librarian that I've seen before include "Person in charge of books etc" , "job!" , "Bibliothecary" , "One dealing with books" , "Person working with books" .)