The Japanese sign in the aikido dojo says Habu Yakkyoku in Japanese which means Lance-Head Snake Pharmacy.
The aikido-gi worn by the young Japanese student (Doni) was right-lapel up which is worn only by the deceased.
The city of Berlin remains named as such. In reality, Hitler hated that name, and had he won the war, the city would have been renamed "Germania".
The Mediterranean Sea is said to be "drained" in this story and its land converted to farmland. Besides being a salty sea and thus unusable for farming for decades or even centuries, the deepest part of the sea is over 17,000 feet making impossible for this to be done, even using 21st century technology.
Many Nazi soldiers - such as the party which arrests Wegener - are carrying Heckler & Koch MP5 submachine guns or variants. Although it is a German weapon, the HK MP5 was only adopted by German police and military forces in 1966. This would be anachronistic if the series took place in the 'real' 1960s, however this is an alternate history where events took place very differently.
The total population of both Germany and Japan in the real 1940 was actually 5 million people less than the total US population. Besides the US' manufacturing base exceeding both nations, the population difference would have made their ability to conquer the country exceedingly unlikely. The history of the series' universe is different than that of reality, and takes place in a timeline where this was clearly not an impossibility.
Canon City, Co is consistently mispronounced as Cannon City while Canon should be pronounced Can-Yun. Due to some obscure typographical reason, the original "Cañon City" became "Canon City" in print -- but Coloradans still pronounce it correctly ("Canyon").
Imperial units are still used in the U.S. Reich. It is not likely that the Germans would allow for such duality of measuring units and would probably instead unify their sphere of influence on the DIN standard which uses the metric system.