The swastika is widely known as a Nazi emblem (regardless of its origin), and is delineated in German law as the symbol of an unconstitutional organization. Public use of a swastika carries a penalty of up to three years in prison plus a fine. Ubisoft created censored versions of The Stick of Truth for the EMEA regions and Australia, and it was working on a special version for German markets.
Something must have gone wrong, as The Stick of Truth's German Steam page today carries the following message:
"We're sorry to inform you that we are unable to deliver your pre-ordered version of South Park: The Stick of Truth on March 6th as initially planned. The German and Austrian version of South Park: The Stick of Truth contains an unconstitutional symbol which means that we are unfortunately not able to release the game on the German and Austrian market at this time. This concerns all versions / platforms of the game. There is no need to amend or cancel your pre-order. A new release date of South Park: The Stick of Truth for the German and Austrian market will be announced shortly, and we will ensure that your order is delivered to coincide with this new date."
There's only one rule, and it looks like Ubisoft broke it: Don't mention the war.