Criminal mob with sly character (6)
I believe the answer is:
symbol
'character' is the definition.
(I've seen this before)
'criminal mob with sly' is the wordplay.
'criminal' is an anagram indicator.
'with' means one lot of letters go next to another.
'mob' put after 'sly' is 'slymob'.
'slymob' anagrammed gives 'SYMBOL'.
(Other definitions for symbol that I've seen before include "Emblem or sign" , "Emblem, icon" , "Meaningful character" , "Something that stands for something else" , "Character or glyph representing something" .)