I did some Google searching, but I couldn't find a specific definition for 3 short/1 long. The closest I could find was 3 short by itself which meant that the ship was going to start moving astern, which clearly doesn't apply to a ship heading forward to leave port.
Does anyone know if there is a special meaning for this combination? I'm figuring that it may be possible that it's not a standard combination and is being used as a greeting. In which case, I am thrilled that the Master of the ship is deciding to say hello to those of us on the webcam.
I haven't noticed it from other ships yet, just the Monarch of the Seas. She should be departing soon from Port Canaveral, so if you tune in right away, you might hear the horn on the webcam today.