"In God we Trust" is imprinted on every United States coin and dollar.
Where in the world this model was directly adopted from, I am not quite sure. Britain, Spain, France, Greece, Rome. But where this system first existed is south of the Sahara desert and west of the Red Sea in the East of Africa.
Around 330 C.E., King Ezana converted to Christianity, converted his Nation the Axumite Empire to Christianity, and had a greater vision to convert nations outside his own. So, to spread his religion he used the most frequent and widespread traded good - coins. King Ezana ordered his court to replace the crescent symbols on the coins to the cross. In the next two centuries, other great Empires including the Roman Empire adopted this system and used phrases like 'By the grace of God' and 'Christ is with us.'
Before the Christian era, before King Ezana, the Axumite Kingdom used coins with the face of King Endubis. Around 270 C.E., King Endubis wanted his kingdom to better participate in the fast-paced Greco-Roman trade across the Red Sea. So, the writing on the coin is in Greek letters and the weighing system of the coin is Roman. The Axumite Empire is the first pure African nation to adopt a coin system.
Source: Ethiopianhistory.com