a light, dilute spray of a dust type color (perhaps buff of light tan) will go a long way towards doing this.

You can try sanding the front of the poster with very fine sand-paper. Staining with diluted washes also works. You can try tearing a corner off, or CAREFULLY burning the edges. The burning technique is easier with larger posters. Vary the amount of weathering because some posters will be newer than others. Also try overlaying one poster over another with just an edge sticking out from underneath. Hope this helps.

I've done ration cartons using pigment powders and/or chalk pastel colors. seemed to work fairly well.

Damien, I use one of two methods. My favourite is to take the printed out poster, and roll it diagonally from one corner to the opposite (top right to bottom left), very tightly, like a very slim joint. Then unroll it and repeat from the opposite angle (top left to bottom right). Then flip the poster over and do the same thing on the reverse. This'll make the printed ink crack and look worn. Then paste it onto the wall or door or wherever it goes on the dio and rub some pastels in to make it look like dust from the surroundings. How much dust depends on the terrain. It should look like this:



If you prefer the poster to look really faded and worn (as if it has been in wet weather), do the same as above, but then soak )for about half a minute) it in a mix of water and white glue before sticking it on. The water will wash out the lighter colours and leave only the darkest tones, giving you this result:



Take extra prints and experiment.