I’ve recently finished a course on Macbeth and Othello, and I’ve been doing some research. James I was king at the time, and he wrote a book called Demonology, which was all about witches. Macbeth features witches, so Billy Wagglestaff said to his manager, “Why don’t we try and get the king along on opening night to do a book signing?”. James thought that would be a great opportunity to flog some books, so that’s what happened. He signed the books Jim 1st because he thought that would be less formal than James Rex. He did think of styling himself Jimmy Stuart but his courtiers told him that that could lead to confusion.

I’ve drawn a picture showing what the book signing set-up might have looked like:

I feel duty-bound to admit that none of the above is true as far as I know.