I've never seen them. It doesn't surprise me. Trigraphs were added to support machines without full ASCII support, lacking characters like ~ # { } and so on.

I've never seen them. It doesn't surprise me. Trigraphs were added to support machines without full ASCII support, lacking characters like ~ # { } and so on. Such machines are extremely rare, in practice. For example, even an early 1980s Apple //e, has those characters on its keyboard and in its character set.