Sign of fashionable writer (8)
I believe the answer is:
inscribe
'sign' is the definition.
(inscribing is a kind of signing)
'fashionable writer' is the wordplay.
'fashionable' becomes 'in' ('in' can be similar in meaning to 'fashionable').
'writer' becomes 'scribe' (scribe is a kind of writer**).
'in'+'scribe'='INSCRIBE'
'of' acts as a link.
(Other definitions for inscribe that I've seen before include "autograph" , "Engrave; dedicate" , "Engrave; enter (name in list)" , "chase" , "Scratch" .)