Star sign Aries? Tsk, that’s wrong (8)
I believe the answer is:
asterisk
'star sign' is the definition.
(symbol resembling a star)
'aries? tsk that's wrong' is the wordplay.
'that's wrong' indicates an anagram.
'aries'+'tsk'='ariestsk'
'ariestsk' is an anagram of 'ASTERISK'.
(Other definitions for asterisk that I've seen before include "Star-shaped symbol as reference mark." , "Star in print" , "Character drawing attention to footnote" , "Printed star" , "Sarkiest (Anag)" .)