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.

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As with most communication unless both sides know what is being said, there is no effective communication.  I would hazard to guess that most service people and most patron wouldn't be able to effectively communicate.

Wow, this takes me back to when I would frequent American fine dining places. It was handy to have a code for them not to take my meal when I left the table ("pause" ), but I suspect it's not practiced at more than a few places these days.

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.

Sign language for utensils - who knew?