That would be considered counterfeiting.
The True we use is standardized version of the King's coin. All you would get out of this would be jail time.
I presume that all coins have a seal, and some kind of imprint on them to make them Trues.
Blackguy, I think you have misread. He is not making coins, but melting them down back into gold. Which I am sure would take a lot of coins due to the fact that there is probably not a lot of gold in the alloy, anyway.
However, the abiilty to do this was used in the older days when people would melt coins, urns, or what not just for the metal (not necessarily gold from gold coins). Then the metal was used for making other things. It was like old world recycling. Some metals were rare or hard to get. So they took something they did't need and made it into something they did.