Sign of gold leading to plot (9)
I believe the answer is:
autograph
'sign' is the definition.
(I know this)
'gold leading to plot' is the wordplay.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'leading' is a charade indicator (letters next to each other) (some letters go in front of others).
'plot' becomes 'graph' (graphing is a kind of plotting).
'au'+'to'+'graph'='AUTOGRAPH'
'of' is the link.
(Other definitions for autograph that I've seen before include "One's signature" , "Famous person's signature" , "a collector's item perhaps" , "Sign" , "One's signed" .)