The rest of the people in the restaurant also laughed, and took pictures. They stopped laughing after a few minutes, though. The owner also gave me some friend squid just because I was funny.
When I wore this t-shirt at work at the university, three women who work in our cafeteria saw me when I was standing in line at the coop shop (they were standing in line at the other cashier). They also laughed. A lot. They laughed while they were waiting in line. They kept laughing while leaving the store. They laughed when they walked up the stairs, and they were still laughing when the disappeared down a corridor in a direction we were not going...
My Greek colleague thought they were laughing too much, haha. His opinion is that since it is just a factual statement, which is a true one, and not a joke, why would you laugh at all. I suggested it is because it is so obvious that I am not Japanese that stating the obvious becomes funny. We then discarded this theory, because no one is laughing at all the fire extinguishers that are marked "Fire extinguisher" even though it is obvious what they are, or the "Automatic door" signs on the obviously automatic doors, etc.