@BillRM,
Besides that, Christianity became the state religion in 301 AD in Armenia, that#s some years before it became tolerated in Rome and three dozen years before Constantinus was baptised. (In the
Empire of Aksum, Christianity became the state religion earlier than in Roman Empire as well.)
Though I do agree that states can/could give any Christian symbol the meaning of an "official" symbol, I'm not aware any "official" symbol by the early Christian church or it's follower-ups like the Catholic church, the Orthodox churches etc.