As you can tell from the script, the sign means there is an elevator. Howeve neither speaker ever says the word "elevator." They don't need to. By their talking about the floor the office is on and talking about going up, the listener is able to understand what they are talking about and consequently what the sign means. For that reason, asking the learners, "How did you know? 2) is probable just as important as whether or not they got the correct answer. It makes th aware of the clues that gave them the meaning. It also provides information a an example for students who may not have gotten the correct answer.