Tough para’s unusual signature (9)
I believe the answer is:
'signature' is the definition.
(autograph is a kind of signature)
'tough para's unusual' is the wordplay.
'unusual' indicates anagramming the letters.
'toughpara' anagrammed gives 'AUTOGRAPH'.
(Other definitions for autograph that I've seen before include "A signature given as souvenir" , "a collector's item perhaps" , "Famous person's signature" , "One's signature" , "(Celebrity) signature" .)