Signal to include large hint (4)
I believe the answer is:
clue
'hint' is the definition.
('clue' can be a synonym of 'hint')
'signal to include large' is the wordplay.
'signal' becomes 'cue' (I've seen this before**).
'to include' indicates putting letters inside.
'large' becomes 'l'.
'cue' going around 'l' is 'CLUE'.
(Other definitions for clue that I've seen before include "Hint to help the solver" , "Aid to puzzlers" , "What's this" , "Helpful hint" , "Hint, tip" .)