Rule 903 Subscribing Witness’s Testimony

If you signed a document as a witness, you generally do not need to show up in court to prove that the document is real. Most of the time, other methods can be used to show a document is genuine without calling the person who witnessed it.

The only exception is when a specific law requires a witness to testify. This might come up with certain documents like wills, depending on what state's laws apply to that document.