Indicator shows gold in egg shape (5)
I believe the answer is:
gauge
'indicator' is the definition.
(thesaurus)
'gold in egg shape' is the wordplay.
'gold' becomes 'au' (Au is the chemical symbol for gold).
'in' is an insertion indicator.
'shape' indicates anagramming the letters.
'egg' with letters rearranged gives 'gge'.
'au' placed within 'gge' is 'GAUGE'.
'shows' acts as a link.
(Other definitions for gauge that I've seen before include "Measuring instrument" , "Measure - estimate" , "Distance between the rails of a railway track" , "Measuring device" , "Rail track width" .)