When I was little I went to a Military School for the summer, we were all supposed to follow certain rules and there are only two of these that I recognize. The first and last.
I'm adding another picture because that one was too small to read on my phone.
Answering your question, I would have to say with the exception of the one called finished I don't use any of them. The vast majority of restaurants I go to do not have wait staff that would know what they meant anyway.
I've never seen/heard of this and I rather doubt that 99% of the servers at most restaurants have ever seen/heard this either.
Also, I can just speak my intentions rather than resort to some utensil secret code.
It may originate from when the help wasn’t allowed to speak or make eye contact with the upper crust. A traditional worth ignoring.
@Garban Ah, okay. Well, I'm certainly not upper crust. I'm not even sure if I qualify as middle crust.
@Charles1971 I’m just old and crusty.