Blurred mark (6)
I believe the answer is:
smudge
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">blurred mark</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for smudge that I've seen before include "Soil - daub" , "Choking smoke" , "Blotch" , "A smeared mark or stain" , "blurred impression" .)