Posters do not work in the main because the general travelling public are a bit thick. Only the other week my control room was overrun with calls from the helpline asking where their trains were even though we had posters up prominently at the entrance and the platforms informing passengers.
Are you sure that's not just because the information wasn't where people expected it to be?
Speaking as one of those railway enthusiasts with our silly opinions, I found myself wandering through Leeds City Station today, and as you would expect, there were several rows of information screens.
The first one on the Wellington Concourse included four boards, two showing a list of departures, one showing a list of arrivals and the other showing the safety information (I use the word "safety" in the loosest possible way obviously) alternating between the "train doors close a minute before departure" and the "unattended items will be exploded" messages.
These are the only screens on the Wellington concourse, so if everything you and other posters on here are saying is correct, the Wellington concourse must be either:
a) an accident/insurance blackspot responsible for putting train fares up by an as yet unproven percentage.
b) some sort of unexplained twilight zone where neither the laws of the land pertaining to insurance claims apply, nor the normal laws of human activity which cause people to fall over when running for trains or leave unattended packages around the place.
The alternative, of course, is that it is perfectly possible to display the "safety" information alongside the departure information and satisfy all health and safety requirements.
Here's an idea - why not have an encased poster either side of all platform departure boards. One could have the doors closing sign and the other could have the unattended packages notice. That way you can display the "safety" information to the satisfaction of the judiciary whilst the rest of us can actually see where the train is going