Distinguishing mark of each criminal imprisoned by court (6)
I believe the answer is:
cachet
'distinguishing mark' is the definition.
(I've seen this before)
'each criminal imprisoned by court' is the wordplay.
'criminal' indicates an anagram.
'imprisoned by' is an insertion indicator.
'court' becomes 'ct' (abbreviation used in road names).
'each' is an anagram of 'ache'.
'ache' going within 'ct' is 'CACHET'.
'of' acts as a link.
(Other definitions for cachet that I've seen before include "Distinguishing mark or seal" , "Kind of prestige, from France" , "Mark of approval" , "Prestige - seal of approval" , "Feature or quality conferring prestige" .)