Figure out a good symbol (5)
I believe the answer is:
token
'symbol' is the definition.
(I know that token is a type of symbol)
'figure out a good' is the wordplay.
'figure' becomes 'ten' (ten is a number or figure).
'out' is an insertion indicator.
'a good' becomes 'ok'.
'ten' placed around 'ok' is 'TOKEN'.
(Other definitions for token that I've seen before include "Counter" , "Indication, symbol or voucher" , "Sign, maybe substitute for the real thing" , "Done for appearance's sake" , "Nominal - souvenir" .)