I agree with jackdale that the responsibility is a shared one.
You have every right to drift your boat most any where you wish, as long as you keep a watch.
In a constricted waterway, this isn't a good decision though.
If the guy that is on a collision course isn't keeping watch, they are derelict in their responsibilitys, in short someone has to be running the boat in a responsible manner.
Situations are varied, I really think that a signal reminder is NOT a bad thing, if used to elicit some response from a boat that otherwise seems to be running unattended, if they complain about that,sorry!
I do remember smallboatlover saying the vessel looked to him , unattended.
Lots of great input here!!