Initial clue (4)
I believe the answer is:
sign
This clue is a double definition.
'initial' is the first definition.
(thesaurus)
'clue' is the second definition.
(I know that sign is a type of clue)
(Other definitions for sign that I've seen before include "Traffic control - to write one's name" , "part of the zodiac" , "Communicate to the deaf" , "Engage by written agreement" , "As the star was for 14 across" .)