[dada78641]

I don't think this signal becomes useless the moment an attacker knows about it. It's one thing to prevent your victim from speaking to anyone unattended, but it's hard to imagine there never being a moment for them to make a quick hand gesture to the outside world. At some point an attacker has to take their eyes off their victim even if for just a moment.

It's true that attackers can take precautions against this, but that also makes their attack harder to carry out.