Mark of disgrace (6)
I believe the answer is:
stigma
'mark of disgrace' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for stigma that I've seen before include "Mark of shame or social disgrace" , "Part of a flower" , "Mark of infamy or disgrace" , "Mark of shame, stain on reputation" , "Bad mark" .)