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Pipes are quite common, but for tricky data, I'd recommend ¬. It's on most keyboards and I can't think of any other use of it.

This symbol is not present on US keyboards.

I did not know that. It's on most UK keyboards

What is it called? What's it for?

I had to look it up as I don't know what it's called and it's a negation symbol https://en.wikipedia.org/wiki/List_of_logic_symbols

As to what it's for, I'd say it's great as a delimiter. I've never used it for its intended purpose.