One thing that caught me off guard one time while in the classroom was the different meanings of certain shapes across cultures. I was standing at the blackboard, the students having chalked some answers up there. As I read the first answer, I checked it off and nodded, and threw in a "Very good." The students looked puzzled, and several touched eraser to paper.
Apparently, check marks are not used in Japan to denote a correct answer. As I learned that day and would come to observe quite frequently in the future while watching teachers grade tests, correct answers get a circle beside them (○＝まる) and incorrect ones get an X (ばつ) or often just a straight line (that sometimes resembles a check mark, I guess).
Additionally, triangles (⊿＝さんかくけい) are often used to denote partial credit or "debatable."
I've seen these symbols used at my current job, too. At our daily morning meetings, we each present some articles and talk a bit about them, and then my boss tentatively draws a circle, x, or triangle on his paper next to the article name to note whether or not the news will be sent to Tokyo (the triangles are "maybe").
|And blue moons mean "%$^ you!"|
In retrospect it makes perfect sense, but it just never occurred to me that different shapes and symbols take on different meanings depending on the culture.