In my opinion 3D environments are a really
[mod edit] You've been here long enough to know better than to star out swears[/mod edit] way for presenting detailed information on posters. A way to do this is to put up the sign and also have a trigger zone in front of it. When the player moves close enough to the poster the image is also displayed on the screen in full size. An audio file can be played along with the full size image.
I have a script for doing this on my other pc. Will look for it when I get to it (don't hold your breath though).