@DougMac... explaining the downvotes
Having lived in the US for a few years (in various places) but being a brit ... so i noticed these things... The 'nobody calls it a pound sign' is VERY strongly regional and/or local.
Some places assume if you say pound sign you mean Lb, and call # 'a number sign', others almost exclusively use it as a weight identifier " #potatoes 39c " isn't a weird hashtag, it's telling you the tubers are cheap