Koreans won't pay any attention to your note. It's unfortunate, but it's true. I've heard of dozens of instances where foreign visitors have gone to the trouble of getting some cards printed up that outline their allergy to nuts or shellfish and Koreans simply smile and nod and then serve the person food that makes their throat close up and then act as though they're completely mystified as they're rushed off to hospital. While I'm not suggesting that having some cards would be completely useless, I am telling you that these are not kind, considerate, compassionate, worldly, understanding, sympathetic people we're talking about. Food allergies are not common in Korea, and I'm guessing that's because they've been bred out. These people will eat literally anything. They'd eat shite on a shingle if you told them it was traditional Korean food that's good for your health. Stick to simple dishes like grilled meat so you don't have to worry. Koreans don't go out of their way for anybody, not even each other. Nobody is going to double check with the chef that your food meets your specifications, so be responsible and choose your meals wisely.