It's a bit like how a lot of people refer to '#' as 'hashtag' these days, without knowing about 'the pound symbol' or 'sharp' (if you are a musician). :)
I had a web design professor who said its "true" name was octothorpe, and while various sources confirm that, I've never heard anyone else call it that. Another student in the same class once called it the "tic tac toe symbol."
Ok, the true pedants can tilt their head a little to see the difference between a # and a [Edit: Hmm it seems HN doesn't support pasting of extended characters such as the musical 'sharp'?!?]...
I will have to change the pronunciation in my C# programming books to 'C-hash' instead of 'C-sharp'... :)
An octagon is a shape. A stop sign is a symbol that happens to be an octagon. Inversely, an octagon in the context of street signs represents "stop."
The octothorpe, used in music, represents "sharp." In front of a number it represents "pound." In front of a string on twitter it represents "hashtag."
AFAIK the typographical/visual differences are basically irrelevant. It's just a different symbol with a different meaning in different contexts, all represented with the same shape.
Yes, the pound sign is different than the sharp symbol, just as single quotes are different than apostrophes, and guillemets are different than less-than and greater-than symbols, and the flat symbol is different than "b".
Now, limitations of first common US typewriters and then the ASCII character set have led to conventions where some of these have been used in place of the other because the correct symbol wasn't available, but that's different than the symbols being the same, and in most modern contexts, the correct symbol is usually available.
# - octothorpe [2]
Different symbols, though very similar.
(Edit: So much so that the true sharp symbol apparently does not render correctly on HN)
IMO, yeah, maybe not the best choice by MSFT. But pragmatically, we all know what "#" means in that context even if it's not correct. All the Monday-morning-quarterbacking in the world isn't going to change that. So I'm as all for an academic discussion as the next person, but that's all it is.
To hash means to chop up, which is a possible origin. To [cross] hatch means to colour in a space with [crossed] parallel lines, which is also possible.
(I know you know this. Others probably don't.)
It's as if people who call # the pound sign are from the UK and typed shift-3 on someone else's keyboard without actually noticing what showed up on the screen.
I've always known # as representing "number", which is why you see it in lists: #1, #2, #3 etc.
A symbol that, after many decades of living in the U. S., I'm seeing for the first time just today. In my experience, if it's not written as "lb." or "lbs.", a hash is often used: "#".
# is never, ever, ever called the "pound sign" in Britain or Ireland. That's always £.
#prescriptivism.
I think I have some Googling to do. :)