Cabin sign I add displaying emblem (8)
I believe the answer is:
insignia
'emblem' is the definition.
(insignia is a kind of emblem)
'cabin sign i add displaying' is the wordplay.
'displaying' indicates a hidden word.
'INSIGNIA' can be found hidden inside 'cabin sign i add'.
(Other definitions for insignia that I've seen before include "Stars and stripes, say" , "Badge worn to show official position" , "Badge or emblems of office" , "Badge of membership" , "military mark" .)