When did they start stamping In God We Trust on US Coins?

Answer 1

The motto was first used on the 2-cent coin that was introduced in 1864, largely in response to the Civil War. It was placed on other denominations gradually, and usually only as part of an overall design change. For example, the motto didn't appear on nickels until the Jefferson design was released in 1938.

Paper bills did not carry the motto at all until the 1950s. The anti-communist hysteria of the time led to a movement to put the motto on all currency to show our distinction from the "godless communists". It was first put on dollar bills in 1957 and was added to other denominations during the 1960s.

The motto remains contentious to people at opposite ends of the faith spectrum, with small groups of atheists and agnostics continuing to call for its removal and with other strongly religious organizations upset over the motto's supposedly small size and/or positioning. It is of course mostly a non-issue to the vast numbers of people in the middle.