So long as everyone knows the signal, I suppose the clearest word is best. If someone shouted fire in the middle of the sea, that would certainly attract your attention. If you live where there are breaking waves, rip tides are a possibility, even if they have never caused an emergency in the past. I don't know why breaking waves are a necessary factor.
Breaking waves drive water before them, and that is the "engine" that pumps water into the shallow area; it is then returned to the sea through the narrow gap. That return current, if small and intense enough, is a riptide. Without breaking waves water is not pumped into the shallow area. (Regular ocean waves don't move any water; the water just stays in place and moves in a circle.)
Why waves "break" is sort of interesting. The wave has many components of shorter wave length in it. These shorter wave length componets travel faster than the fundamental component of the wave - dispersion but not very noticeable until the wave gets into shallow water (near the shore) Then the fundamental component "feels bottom drag" and slows down its speed some, but the shorter componets don't. Relative to the fundamental, they "race ahead" steepen up the wave front and finally get ahead of it but then with little under them they fall down - that is what a "breaking wave" is.
It appears that riptide killed my high school English teacher on vacation around Myrtle Beach many years after I graduated. The cause of death was given as drowning.
On most beaches, they appear and disappear quickly and regularly. So safe swimming areas often move up and down patrolled beaches. On beaches with long term or what they refer to as permanent rips, they usually have signs pointing where they are and flags indicating safe swimming areas. At least this is the case here on the open surf beaches in Queensland. I am not sure of the policies around the rest of the world. I do think that learning what to do in a rip should be part of any child's swimming lessons. Especially to teach and explain to children what it feels like and that they should not panic. The same should apply for adult swimming lessons as well.
Shh.. My response apparently offended his sensibilities. It's all good though. I removed the quote. Let's move on shall we...