if that was the case, i could hang a swastika flag in my garden: "it's based on historical events and therefore appropriate". actually, those historical events are what makes it inapproriate in the first place ^^
if someone doesn't like you, he might call the police on you... but it's unlikely something would happen, and as i said earlier... unless someone actually tells on you, nothing will happen.
but, i have to correct you here arne, the law does not state anything about no punishment for minor cases (§86 StGB does, §86a StGB does NOT though, and most likely §86a is the one that would be more appropriate here (propagandamittel would probably be things like "der stürmer", "mein kampf" etc. while §86a explicitly is mentioning flags, uniform(parts) etc.)... i'm not a lawyer though ;-))...
What are you talking about? The game is set in world war 2 like so many other games and films and therefore for historical accuracy the swastika and all other nazi symbols of that time should be used. It would look stupid without them. Everyone playing these games and watching films about nazi's or whatever should understand that so what's the big deal? It's history whether you like it or not. Also your example of putting a flag outside today in your garden is off the subject...