The letter of their law regards propaganda; materials prepared and distributed with a political interest.
While one might argue that the display of this on a historical boardgame would be a form of agitation or propaganda, this is quite a difficult argument as the game does not actually aggrandize or promote one ideology over others, quite the contrary, it has them all compete somewhat fairly against each other, and has very little ideological or dogmatic content of any kind.
Nevertheless, the chilling effect of such a speech-restrictive law (that people will not display the symbol even if they have a carved-out exception or the statute explicitly does not appear to apply) is that it would be more cautious and to avoid displaying it, or anything like it, in order to avoid scrutiny, or criticism (these are at the heart of PC, which is not a really a legal phenomenon but one of social taboo and propriety).
Since it adds little to display it, or any other prohibited or restricted symbol, there isn’t a particularly good reason to do so, not for marketing, historical accuracy, etc. Even the Ironkreuz flag, which is a cross, is just as evocative for most modern people, any symbol can be banned under the code 86 its not a list of symbols its a prohibition on their intended use…