The first sign (7)
I believe the answer is:
initial
This clue is a double definition.
'the first' is the first definition.
(thesaurus)
'sign' is the second definition.
(initial is a kind of sign)
(Other definitions for initial that I've seen before include "Occurring at the start" , "Name's first letter" , "Primary" , "Introductory" , "Occurring at the beginning" .)