The "OK" sign that is commonly used in western culture to signify that something is alright or that you've 'got it' is a very offensive gesture in Japan. In Japan this gesture relates to money and often means that a person is trying to get more money out of a business deal.
If a Japanese business person sees this sign being used toward them they may become highly offended thinking that their fair monetary offer is being looked down upon. Many gestures mean different things depending upon the culture in which you are using them in. Its important to be careful about using gestures when dealing with other cultures.