With graffity and advertising posters one of the issues is licensing. The result is quite dull. Fake posters and repeating graffity in the game. I think it would be awesome if players can create their own posters and like liveries put them in the game. Just like the livery editor. There is no need to provide the graphics tools for it, just the interfacing would do.
On the other hand, it would be great to use some shared libraries. It has always seemed difficult to me that it is necessary to establish some author's rights because it is long and unclear. When I work as a designer, I don't bother about this because I'm too lazy to make a watermark. You can use vintage posters service to avoid the mess with copyrights too much and make your work quick and easy. This is just right for beginners or those who want to make a poster without contacting designers.
