Setter's new and unusual RIP sign is thought-provoking (9)
I believe the answer is:
inspiring
'thought-provoking' is the definition.
(inspiring can mean provocative or stimulating)
'setter's new and unusual rip sign' is the wordplay.
'setter' becomes 'I' (the person that set the crossword).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'and' is a charade indicator (letters next to each other).
'unusual' indicates an anagram.
'rip'+'sign'='ripsign'
'ripsign' with letters rearranged gives 'spiring'.
'i'+'n'+'spiring'='INSPIRING'
'is' is the link.
(Other definitions for inspiring that I've seen before include "Breathing in or activating the mind" , "Impressive" , "Breathing (that's encouraging!)" , "Animating; uplifting" , "Filling with confidence, stimulating to achievement" .)