After signal, shout 'open' (8)
I believe the answer is:
flagrant
'open' is the definition.
(thesaurus)
'after signal shout' is the wordplay.
'after' says to put letters next to each other.
'signal' becomes 'flag' (flag is a kind of signal).
'shout' becomes 'rant' (I've seen this in other clues).
'flag' put next to 'rant' is 'FLAGRANT'.
(Other definitions for flagrant that I've seen before include "Shocking" , "Of unconcealed outrageousness" , "Blatant, outrageous" , "Being shameless" , "Openly outrageous" .)