A PET exam task

[Mayflower]

Good part of the day, everyone.
I am a non-native ESL teacher based in Russia. Would anyone aware be so kind as to explain me some issues concerning Reading Part 1 in PET exam?
Namely, the Silence, please! Exam in progress sign.

The task is: "What does the text say?"
The three answer options provided are the following:

A) You mustn't speak during the examination.
B) Please respect others and remain quiet during the examination.
C) Do not talk to the teacher.

The things that got me confused were:
1. The correct answer option was A, which means the sign is aimed at the students taking the exam, i.e. students in the exam room. Is that always true?
2.Do you ever put similar signs outside the door (I mean, literally attach it to the door or next to it) for people outside the room to keep quiet?
3. Doesn't "please" imply the correct answer should be B?

What is your view as native speakers?
I would be glad to get your answers!
Thank you in advance, everyone!