Husband wearing small wig -- a sign he doesn't care? (5)
I believe the answer is:
shrug
'a sign he doesn't care?' is the definition.
(a shrug indicates a lack of interest)
'husband wearing small wig' is the wordplay.
'husband' becomes 'h'.
'wearing' is an insertion indicator.
'small' becomes 's' (abbreviation - e.g. clothes size).
'wig' becomes 'rug' (rug is a slang term for a wig).
's'+'rug'='srug'
'h' going into 'srug' is 'SHRUG'.
(Other definitions for shrug that I've seen before include "Gesture expressing unconcern" , "Show no interest" , "Gesture of resignation" , "Gesture of uncertainty or not knowing" , "____ off, dismiss" .)