Perhaps this belongs in another forum...but it just got to me today, watching the Rice confirmation hearings:
A person stands in front of a jurisdictional body (congress, a court, a tribunal...), and swears by GOD to tell the truth.
As an aside, after the testimony, they may well rent a taxi and pay the driver with a currency that says "In GOD we trust."
Now, I've only once been called to testify in a court, and I was, at that time, more than willing to say "so help me god."
Now, I'd have to decline to make that oath.