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.
@Garban Ah, okay. Well, I'm certainly not upper crust. I'm not even sure if I qualify as middle crust.