Kevin Kruse explains how “in God we trust” began to appear on coins and stamps—it’s more recent than you’d think:
“So the phrase “In God we trust” comes from an often forgotten stanza of the “Star Spangled Banner.” It goes: “Then conquer we must when our cause it is just, and this be our motto – ‘In God is our trust.’” That stanza was largely forgotten until the Civil War when that phrase “In God we trust” is plucked out of that line and placed on coins. And it is done so at the urging of religious leaders who believe the Civil War has come as a result of America’s original sin, of not officially being founded as a Christian nation. And they ask the Secretary of Treasury to correct that and he does so by placing it on coins.
The phrase appears on coins intermittently over the next 50 or 60 years. Theodore Roosevelt tries to have it removed — he believes it’s close to sacrilege — but the public outcry prevents him from doing so. During this moment of the Eisenhower years, the phrase flourishes and it does so first when it’s placed on a stamp in 1954. Then [in] 1955, Congress decides to add it to not just coins but to paper money. And in 1956, they move to make it the country’s first official national motto.”