Dirty mark or marks scorch clothes (5)
I believe the answer is:
smear
'dirty' is the definition.
(smearing is a kind of dirtying)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for smear that I've seen before include "allegation" , "Unwarranted accusation" , "False report" , "nasty mark" , "Medical examiner may take this" .)