The model is UVW mapped to make changing the images simple. A single bitmap contains the three images tiled vertically. Simply paste your image, scaled appropriately onto the provided bitmap and you're done.
A rotation dummy object is used to control the movement of all of the platens simultaneously (using an instanced rotation controller). To animate the sign changing simply rotate the dummy through a 120 degree angle.
The bulletin board is equipped with an access ladder, four planked walkways for ease of access, and two top mounted lights to make it visible in the dark.
Make sure to download the free animation if you're interested in seeing how it works.