What does the pound sign mean when it is used in a sentence?

[John P]

In Britain we call that sign "hash". In Britain the sign "£" is a pound sign, meaning our major unit of corrency, slightly larger in value than the dollar or euro - e.g. £100 means one hundred British pounds. I think that Americans call "#" 'the pound sign' or sometimes 'octothorpe'. In American notation "#" means 'number, as in "He lives at #57 in this street". In Britain we use "No." for 'number' as above noted (No.57).