It's a bit of an odd one. North Americans seem to use it in place of what would be № in the UK, though it seems that's becoming rather archaic now. The naming also seems to be a bit inconsistent, apart from it being the sharp sign in music it was also known as an "octothorpe", and I've no idea where "hash" comes from. One that really confuses me is when people call it a "pound": I don't know if this is anything to do with it sharing the same keyboard position with a £ sign on UK keyboards or just random coincidence (for the record, I never understood the £ either until I found out it's a crossed L for "librae", the Latin currency denomination; I'm not sure how this came to be a pound, though I guess it would also explain why the equivalently-named unit of weight is abbreviated lb).
Well that was a bit of a random meander even for me!
Edit: well to satisfy my own curiosity, the currency unit is apparently so named because a pound of silver would be used to mint 240 coins of the actual currency of the day, so it seems the name stuck, and the connection with "libra" is the Latin phrase lībra pondō, meaning "a pound by weight". Though the mix of modern and ancient terminology makes the translation look a bit odd.
Last edited by vometia; 19/06/17 12:32 PM.