If you are passing " from astern" of a vessel this is called an "Overtaking" situation.
International
Sound and Light signals
Rule 34
Maneuvering and warning signals.
(c) When in sight of one another in a narrow channel or fairway:
(i) a vessel intending to overtake another shall in compliance with Rule 9 (e)(i) shall indicate her intention by the following signals on her whistle:
-Two prolonged blasts followed by one short blast to mean " I intend to overtake you on your starboard side";
-Two prolonged blasts followed by two short blaststo mean "I intend to overtake you on your port side".
(ii) the vessel about to be overtaken when acting in accordance with Rule 9 (e) (i) shall indicate her agreement by the following signal on her whistle:
-One prolonged, one short, one prolonged and one short.
***
Inland
(c) When in sight of one another:
(i) a power driven vessel intending to overtake another power driven vessel shall indicate her intention by the following signals on her whistle: One short blast to mean "I intend to overtake you on your starboard side"; two short blaststo mean "I intend to to over take you on your port side"; and
(ii) the power driven vessel about to be overtaken shall, if in agreement, sound a similar sound signal.
*** If there is ANY doubt as to the intentions the danger signal of 5 or more short blasts must be sounded.
If another boat signals their intention to pass you from astern, you should answer with the same signal if in agreement and maintain course and speed.
You should already be aware of a boat approaching from astern ... your head needs to be on a swivel as the pilot at all times. You need to know everything about your surroundings. If you hear this signal you should probably slow down and let them pass safely. Don't crowd them or try to out run them.
Move to the right or left and let them pass
Depending on which side they intend to pass you on, they should give you and audible horn blast. One blast indicates passing on the starboard and tow blasts indicate passing on the port. Remember to return the same audible horn signal to let them know that you heard them and are aware of their intentions. One blast from them gets one blast from you and so on. The vessel being passed will remain the Stand - on vessel, which means you do not alter your course or speed. They, being the Give-way vessel must alter speed and course to pass.
you go and read the manual and then take your test
Maintain course and speed to allow the faster boat to pass safely.
6,000
"She was supposed to be astern while she was sleeping."
The stern is the back end. Astern is 'toward' the stern.
Do not pass between the buoy and the shore
A low pass signal whose bandwidth is much smaller than its center frequency, such as an AM signal. It is a a signal with its spectrum concentrated around zero frequency.
Depending on which side they intend to pass you on, they should give you and audible horn blast. One blast indicates passing on the starboard and tow blasts indicate passing on the port. Remember to return the same audible horn signal to let them know that you heard them and are aware of their intentions. One blast from them gets one blast from you and so on. The vessel being passed will remain the Stand - on vessel, which means you do not alter your course or speed. They, being the Give-way vessel must alter speed and course to pass.