Slang reflected in gold pub sign (9)
I believe the answer is:
autograph
'sign' is the definition.
(autographing is a kind of signing)
'slang reflected in gold pub' is the wordplay.
'slang' becomes 'argot' ('argot' can be a synonym of 'slang'**).
'reflected' says the letters should be written backwards.
'in' indicates putting letters inside.
'gold' becomes 'au' (Au is the chemical symbol for gold).
'pub' becomes 'ph' (public house).
'argot' backwards is 'togra'.
'au'+'ph'='auph'
'togra' put inside 'auph' is 'AUTOGRAPH'.
(Other definitions for autograph that I've seen before include "(Celebrity) signature" , "One's signed" , "A signature given as souvenir" , "Handwriting" , "a collector's item perhaps" .)