Deceive the gangster with the signal (8)
I believe the answer is:
hoodwink
'deceive' is the definition.
(hoodwinking is a kind of deceiving)
'the gangster with the signal' is the wordplay.
'the gangster' becomes 'hood' (I've seen this before).
'with' says to put letters next to each other.
'the signal' becomes 'wink' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'hood'+'wink'='HOODWINK'
Can you help me to learn more?
(Other definitions for hoodwink that I've seen before include "Con" , "Deceive - cheat" , "Deceive, trick" , "Deceive, fool" , "Put wool over eyes of" .)