[Bender]

So having a signal for switching mediums is something that I feel indicates thinking in the wrong direction.

It's not for everyone. I grew up with code phrases. My mom knew that if I said "I love you" to send in the cavalry. We had similar processes in the military. If I answered the phone a particular way they knew the remote site was under siege.

[impossiblefork]

That's an okay use, but in that use you're not attempting to achieving privacy.

Everyone knows you talk to your parents, but code phrases are not a way to get privacy.

[Bender]

It's not for privacy in the way you may be thinking. This was long before cell phones or the internet existed and the conversation would have been over the rotary phone and it is assumed someone is in the house with me that should not be. Goal being police have authorization to kick down the door and assist the person or people that are nutritionally deficient in lead.