Don't play dumb, David. The list of signers is extraordinary and surprising, especially to people like us who actually work in the field. This isn't a bunch of random Twitter people.
More importantly: your comment leaves the impression that there were notable people in the field who had a problem with the letter. If an expert working in messaging security didn't sign it, you and I both know that's probably just because they weren't aware of it (or, at the time, The Guardian's story).
Maybe I'm wrong (or lacking context), but FWIW I read baby's comment to mean that the public editor's claim that he had difficulty finding non-signers is silly.
It's not silly. I am not at all surprised that The Guardian was ultimately unsuccessful at finding someone reputable that works in this field to contradict the open letter.