Thank you for that bit of insight, ST. I wasn't familiar with the UK layout, but I see that what I said originally is likely the issue now.
Yep, we call it a pound sign. There's a rather odd story about how that came about, but it has to do with old typeset printers and not having a the "LB bar" (℔) symbol (seriously, that's what it was called). Somehow that became # and has been used since.