This certifies that
there have been deposited in
the Treasury of the United States
One Hundred Dollars in Gold Coin
Payable to the Bearer On Demand
The pic above is not 1963 but the principle is the same. The gold and the promise of delivery of the gold is what made the hundred dollar bill of 1963 worth something. Not the paper.
The US notes were taken off the gold standard in 1934.