Is there any data to provide? But going off of common knowledge id say either stop signs or traffic signals
That statement is true.
To be precise, the united states coined both gold and silver in 1873. Before this, gold is the only material that is used to create coin money.
But the cost of production to produce gold coin is really high. Because of this, the government decided to include silver in order to drive the cost of production down in 1973.
