You did hit the real value though. A bible signed by a President could be a real windfall in the future. Heck, some Trump supporter would probably be willing to pay big bucks today.
This is really no big deal. He didn’t bring the bibles to sign and handout. Presidents are asked to sign a lot of items. If someone wanted him to sign there bible, so what. I wouldn’t, but I don’t care if someone else does.