I remember about a year ago I was having a solicitor countersign a legal document and she said I'd need to swear some sort of oath on my "holy book". I chose the Quran. She obviously knew I wasnt Muslim and likely saw that it was all bollocks having to do it in the first place. Then I had to put my hand on it and read aloud from a piece of paper which said "I swear on <holy book name> that the statement I present is factual and true".
Of course I may have well have made an oath on the Chronicles Of Narnia for all it meant to me.