The students in my English class often draw a diamond-shaped figure on the board with a short vertical line in the middle. What is this supposed to mean?

Much beloved by students and a staple of Czech graffiti, this is the kosočtverec (rhombus) and is supposed to symbolize the female genitalia. It is sometimes dressed up with lines emanating out in all directions, standing for you know what. Students are also fond of drawing stick-figured pigs preceded by the name of a teacher or schoolmate.