Posters are often used as props, and many games use such billboards for flora, and even classic video games used them for NPC art to save on custom 3D modeling.
The issue with posters is that if you rotate them off the floor/wall to stick out to suit the purpose of prop, flora, or npcs is that they vanish when viewed edge on - posters can be crossed 90deg to temper the illusion but can result in seeing the double cross images. Videogames long ago solved this by having these poster sprites (optionally) autorotate to normally face the player (client side). This can create the illusion of 3D art using only 2D art