Cons getting signs of approval — nonsense! (12)

I believe the answer is:

fiddlesticks

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'nonsense' is the definition.
(fiddlesticks can informally mean nonsense)

'cons getting signs of approval' is the wordplay.
'cons getting' becomes 'fiddles' (I can't explain this - if you can you should give a lot more credence to this answer).
'signs of approval' becomes 'ticks' (I've seen this before).
'fiddles'+'ticks'='FIDDLESTICKS'

Can you help me to learn more?

(Other definitions for fiddlesticks that I've seen before include "Blast!" , "Bother!" , "tripe" , "Violin bows - rubbish!" , "Bows - nonsense" .)

I've seen this clue in The Guardian.

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