Mouth shows character (5)
I believe the answer is:
delta
This clue is a double definition.
'mouth' is the first definition.
(I've seen this before)
'character' is the second definition.
(delta is a kind of letter of the alphabet)
'shows' acts as a link.
(Other definitions for delta that I've seen before include "Wing shape; Greek D" , "Wide silted river mouth" , "The fourth Greek letter found at river's mouth" , "Extended area at river mouth" , "one's often seen at mouth of river" .)