In the states, there is no law that mandates that a person must swear on any book or under any god. For instance, the ceremony for the presidential oath as outlined in our constitution makes no mention of the bible or other holy book, nor does it say anything about any god. The same is true in the courtroom, you don't have to swear on a bible nor under any god. It's purely customary and makes no difference. In court, simply say that you would prefer to swear or affirm or attest or whatever, I forget what the term is, and they'll go through with it minus the bible.