Sneak giving indication that it is an obvious clue (8,4)

I believe the answer is:

telltale sign

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'it is an obvious clue' is the definition.
(thesaurus)

'sneak giving indication' is the wordplay.
'sneak' becomes 'tell-tale' (I've seen this before).
'giving indication' becomes 'sign' (I've seen this before. I am not sure about the 'giving' bit.).
'telltale'+'sign'='TELLTALE SIGN'

'that' is the link.

Can you help me to learn more?

I've seen this clue in The Telegraph.

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