In episode 5 of Prisma Illya 3rei, we find that Gil has somehow pulled an entire hot springs out of the Gate of Babylon. The walls surrounding it have banners with a number of strange symbols and quintessentially-Japanese words on them.
You can see the symbols for yourself below; some of them are very strange, like the biohazard symbol (☣), the radiation symbol (☢), and a pair of clubs (♣) attached end-to-end. The words are "bonsai", "Mt. Fuji" (fuji-san), "sushi", "bushido", "matsuri", "kami", "sumo", "squid" (ika), "tenshukaku", and "heat haze" (kagerou), plus one on the far-right in picture #1 that is cut off.
I have to imagine there is some sort of joke here I'm not getting. What is it?
(The images are spoilered because naked-but-steam-concealed characters.)