Propaganda strives to depict things which are not true as having already happened. The things which are actually true and obvious to the reader are not worth wasting the poster space.
So, if the propaganda poster depicts happy farmers with their hands full of grain and a caption like "To abundance!", this means that the food situation is rather dire, and it concerns both the people and the government.
If it shows a mighty soldier crushing cowering enemies, this means that the situation on the front lines has reached a stalemate (or that there's no war at all, but the state insists that the enemy will strike soon).
If you see a poster condemning the brutality of the enemy, this means the state cannot stop them, is frustrated about that, and tries to, at least, portray them in a negative light.
In other words, let your posters convey the goals of your government that it can't achieve, but still wants people to think something is being done.
Upd.: posters about enemies can generally mean two things. Either the state wants you to believe it's winning against whatever (when it's not), or it wants you to believe there's an enemy (when they're not a reason for concern). This depends on the composition of the poster: whether or not there's someone to defeat the enemy there.