By "you know this note to be totally reliable" I assume you mean you have a fair idea how it got there (eg you just built a time portal. with the intention of sending through financial advice, and a hand, bearing the same tattoo you have, pushed through with the note) and not that you're psychic and literally know things with 100% certainty? IOW you have a high probability estimate that it's genuine, but not an infinitely high one (seems more realistic and applicable if nothing else.)