Follow notice in exhibition (6)
I believe the answer is:
shadow
'follow' is the definition.
(shadowing is a kind of following)
'notice in exhibition' is the wordplay.
'notice' becomes 'ad'.
'in' indicates putting letters inside.
'exhibition' becomes 'show' (I've seen this before).
'ad' placed inside 'show' is 'SHADOW'.
(Other definitions for shadow that I've seen before include "Dark area from which light is blocked" , "Air of gloom" , "opposing counterpart" , "Inseparable follower" , "Hint, remnant; follow secretly" .)