Carl and Betty designed a slogan (6,3)
I believe the answer is:
battle cry
'a slogan' is the definition.
(I've seen this before)
'carl and betty designed' is the wordplay.
'and' is a charade indicator (letters next to each other) (I've seen this in other clues).
'designed' indicates anagramming the letters (designed with the letters).
'carl' after 'betty' is 'bettycarl'.
'bettycarl' is an anagram of 'BATTLE-CRY'.
(Other definitions for battle cry that I've seen before include "Slogan (for those going into a fight?)" , "jingoistic shout" , "Martial slogan" , "Geronimo, for example" .)