Andy Weir did a thing where he shared a PO box address. You could send him a copy of a book with a return shipping label and note on what you want him to write and he'd sign it, repackage it and send it back. I have a copy of The Martian that says "Look! A pair of boobs! -> (.Y.)" it was one of the funniest lines in the book to me

Oh nice! I only said supposedly because I had read about it before that point, that's nice to hear

Except for one, which was then graded and sold on eBay for over $80k which was supposedly donated to charity

yes