An imperfection in the emblem is hardly noticeable (7)
I believe the answer is:
blemish
'an imperfection' is the definition.
(thesaurus)
'in the emblem is hardly noticeable' is the wordplay.
'in' indicates the answer is hidden within the clue.
'BLEMISH' can be found hidden inside 'emblem is hardly noticeable'.
(Other definitions for blemish that I've seen before include "Stain - defect" , "Stain, flaw" , "Flaw that spoils a thing's perfection" , "Flaw; moral defect" , "Small flaw" .)