Yes, the verbal prefixes to a marine broadcast message are in French...ancient maritime custom, don't argue about Freedom Fries, etc. it just is what it is and let it go at that.
Anyway, Securite, with an accent over the last "e" and pronounced See-CURE-IT-ay, which means "Safety" in French, is used to precede marine safety broadcasts of information regarding vessel operations, such as a bridge opening or closing, a ship leaving a berth, a large vessel entering a narrow channel, a tow of unusual proportions and/or dangerous cargo entering restricted waters, or anything else that amounts to the transmitting vessel basically advising everyone else nearby to stay out of the way. As the previous poster said, it's a heads up message.
The next level, Pan, pronounced "Pawn", is in fact to identify messages which while important or urgent, do not rise to the level of immenent distress or emergency. It may be used for such things as to report impending severe weather, advise mariners of missing persons or overdue vessels and request they keep a sharp lookout for them, report any sightings and render aid if possible, or let anyone in the immediate area know that a particular vessel has suffered an engineering or equipment casualty and consequently is restricted in its' ability to maneuver. (For example, drifting at sea while attempting repairs to the main engine.)
Mayday, the English version of "M'aidez", literally "Help Me", is the marine 911 call. Anyone hearing it should drop what they are doing and attempt to locate the vessel in distress and provide any assistance possible. It is only to be used in case of actual imminet peril to life or property, such as a vessel taking on water, on fire or involved in a serious collision; a man overboard; or a serious medical emergency.
