What will be the indication that God accepted Jesus' sacrifice on our behalf In the OT when the high priest exited the holy of holies alive it was an indication that the blood sacrifice on behalf of the sinner had been accepted by God. 
What is the indication that God accepted Jesus' sacrifice on our behalf.
Was it after the resurrection when he showed himself to believers or will it be when he shows himself at the second coming?
The answer is found in Acts 17:30-31:


  “Truly, these times of ignorance God overlooked, but now commands all
  men everywhere to repent, because He has appointed a day on which He
  will judge the world in righteousness by the Man whom He has ordained.
  He has given assurance of this to all by raising Him from the dead.”


Jesus' resurrection from the dead after dying as a sacrificial lamb is proof that God has accepted Him. Also there is Hebrews 10:12: 


  But this Man, after He had offered one sacrifice for sins forever, sat
  down at the right hand of God,


Jesus sitting at God's right hand also vindicates His sacrifice. God has a place for Him right at His side.