Returned to sign agreement and District Attorney's supplement (3-2)
I believe the answer is:
add-on
'supplement' is the definition.
(synonyms)
'returned to sign agreement and district attorney's' is the wordplay.
'returned' says the letters should be written backwards.
'to sign agreement' becomes 'nod' (I've seen this before).
'and' means one lot of letters go next to another.
'district attorney' becomes 'DA' (abbreviation).
'nod'+'da'='nodda'
'nodda' in reverse letter order is 'ADD-ON'.
(Other definitions for add-on that I've seen before include "Feature supplementing standard model" , "Extra unit, peripheral" , "Optional item as supplement or increment" , "Extra charge" , "Computer peripheral" .)