If propulsion is disabled the vessel is “not under command”.
If just stopped while drifting the vessel is still under command per COLREG :
But it has been tried:
https://www.nautinst.org/resources-page/misuse-of-nuc-signals.html
Depends on the type and coloure of the balls, I resume?? 
How is that relevant?
Did you read the next sentence before replying?:
If just stopped while drifting the vessel is still under command per COLREG
Not to mention the attachments.
How is that relevant?
As above; read attachmernts!!
Neither are the scenario I described so how are they relevant?
OK!! You are right; “That definitely wouldn’t hold up in court”.
You may as well get used to see ships looking like this:
Or like this when in ports with height restrictions:
The term “vessel not under command” means a vessel which through some exceptional circumstance is unable to manoeuvre as required by these Rules and is therefore unable to keep out of the way of another vessel.
The key word is " exceptional " circumstances. Drifting for the purpose of waiting and/or similar and having m/e on standby is not an exceptional situation . See some Admirality courts decisions . By displaying lights and day signals we are not released from he colreg duty. It is same as fishing boat displaying she is fishing ( thus priviliged ) but actually she is just underway using engine and pretending to be awfully busy.
Twice a year a number of sailing vessels visit Ålesund either on their way to or from a sun\mmer of cruising in Svalbard. This is the time when they are heading north.
Here is one of the first this year; Noorderlicht on 28. March:
https://www.starclippers.com/eu/our-fleet/tall-ships/introducing-royal-clipper.html
4-masted barque Pamir:
The Union Steamship Company tried to train as many seaman boys and junior officers as they could in the10 voyages She made under the New Zealand flag mostly between San Francisco and NZ. But she did do one voyage to the UK via Cape Horn. While in London the then Princess Elizabeth and her husband Lieutenant Philip Mountbatten were entertained onboard.
This may need its own thread topic…
… but Saildrones?
