Indication of one's ignorance? (4)
I believe the answer is:
sign
'indication' is the definition.
(thesaurus)
'of one's ignorance?' is the wordplay.
'of' indicates a hidden word.
'SIGN' is hidden within 'ones ignorance'.
(Other definitions for sign that I've seen before include "Pointer - indicate agreement in writing" , "information board?" , "Leo, for instance" , "Omen or indication" , "Public notice; portent" .)