Yes, I know that nobody from Amtrak reads this board. That said, signs aren't rocket science; I can't believe that the idea hasn't occurred to somebody in a position to put one up. I suspect apathy. There are so many problems that management doesn't have the power to fix, it's sad when there's one that they can fix but won't.
Another common-sense suggestion: rather than have the exasperated Conductor lecture pax about bike reservations, just instruct them to call in and get one on the webpage when they buy their ticket.
Amtrak's expectation that pax are born with exhaustive knowledge of their rules and regulations is clearly at odds with reality.