Oh...... With Vaultoro you own the gold you buy and it is stored in Swiss Brinks vaults. The difference is the medium of exchange to buy and sell it is Bitcoin instead of FIAT.
How do you know they don't sell the same gold twice?
To be clear I meant a cryptographic proof for the total gold certificates circulating. I don't know if it can be done, even not in a half satisfactory way.
So the gold reserves around the world has now also ventured in the world of crypto if they can already be traded using BTC. Hmmmm this would be the start of great things ahead.