You are correct in that no one can be certain what form the stake (Greek staurus – stake - translated cross) took.
The Scripture gives no symbol as a sign to support faith; which would indicate that no symbol is required. What the scripture says is:
John 13:35 By this shall all men know that ye are my disciples, if ye have love one to another.
Matthew 5:16 Let your light so shine before men, that they may see your good works, and glorify your Father which is in heaven.
Anyone can exhibit a symbol and bring Christ into disrepute. The sign that we are commanded to give is the example of our lives. This cannot be faked.
The atrocities that men commit under the ‘symbols’ of Christianity should be sufficient reason to disassociate ourselves from symbols. Genuine Christians are known by their fruits not their signs.
Matthew 7:20 Wherefore by their fruits ye shall know them.
I hope you have found this helpful.