Notice mixed gins (4)
I believe the answer is:
sign
'notice' is the definition.
(I've seen this before)
'mixed gins' is the wordplay.
'mixed' indicates an anagram.
'gins' with letters rearranged gives 'SIGN'.
(Other definitions for sign that I've seen before include "add name" , "Leo, for instance" , "Token - symbol - omen - write one's name" , "Public display of a message" , "Manifestation" .)