A canceled project I was working on several years ago had a Propaganda-poster based UI theme. For this, I created a large amount of posters that covered Menus such as Store purchasing categories, Factions, Commodity Management, Character Select, and a large number of other interactions. The Poster format was a great tool for organizing a large, tile-based UI based on carousel formats.
Creation of these posters ranged from painting from scratch, 3d Paintovers via characters posed in 3d, to full on screenshot PO's. I really enjoyed making these assets as I was pushed hard to capture certain flavors per faction, and give them all the general feel of old 1930's-1940's War Propaganda.