Everyone knows the cross-hatched symbol #.
For some it’s the “pound sign” because it has been used by greengrocers as a symbol for “pound” on the little signs pricing fruit and vegetables: .75# (seventy-five cents a pound).
For some it’s the “tic-tac-toe sign” because of the game that uses it as the playing area.
Automated telephone systems instruct us to dial certain numbers, “followed by the pound sign,” a direction that confused me at first because I think of this symbol as the “number sign.”
As if there weren’t already enough names for it, engineers at Bell have come up with an “official” moniker for it: the octothorpe. The “octo” part comes from the fact that the symbol has eight points. No one seems to be able to say with any certainty where the “thorpe” comes from.
European phone companies, like British Telecom, call the symbol a “square,” a term apparently too simple for the North American telephone industry.
On the other hand, rather than use the obvious word “asterisk” for that symbol on the dial, the telephone powers prefer to call it a “star.” Go figure.
For an exploration of the etymology of octothorpe visit World Wide Words.