The 15mm Paint Shack has a couple of pages of German propaganda posters scaled for 15mm. You can print these and use them to embellish your WWII terrain.
A nice touch that can make your WWI and WWII terrain more realistic is to put posters on the walls of your buildings. What you need to do is find a site that has pictures of such posters and save the images using your web browser’s “save image as” option. Then you can resize the image using a paint program — or even a decent word processor (import the image into a blank page, then reasize it by grabbing the handles. Once you have the proper size for your figure scale, print it out with a color inkjet.
All you need to do is find the right site. Fortunately, I’ve done that for you. It’s here.