Rap sheet letters (3)
I believe the answer is:
aka
'rap sheet letters' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for aka that I've seen before include "Notation indicating alternative name - palindrome" , "Notation with initials indicating alternative name" , "Also known as, initially" , "Notation indicating alternative identity" , "Notation indicating alias or other name" .)