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