Starts to share extrovert's good news on sign above bar (5)

I believe the answer is:

segno

I'm a little stuck... Click here to teach me more about this clue!

'sign above bar' is the definition.
'segno' can be an answer for 'bar' (thesaurus). I am unsure of the 'sign above' bit.

'starts to share extrovert's good news on' is the wordplay.
'starts to' indicates taking the first letters.
The first letters of 'share extroverts good news on' is 'SEGNO'.

Can you help me to learn more?

(Another definition for segno that I've seen is " musical sign that should be there?".)

I've seen this clue in The Independent.

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