Sign is put up half covered in gold (5)
I believe the answer is:
sigil
'sign' is the definition.
(I've seen this before)
'is put up half covered in gold' is the wordplay.
'put up' says the letters should be written backwards.
'half' suggests halving the letters.
'covered in gold' becomes 'gilded' (I've seen this before).
'is' back-to-front is 'si'.
'gilded' cut in half is 'gil'.
'si'+'gil'='SIGIL'
(Other definitions for sigil that I've seen before include "Seal" , "Sign" .)