The Free On-line Dictionary of Computing (18 March 2015):
"#", ASCII character 35.
Common names: number sign; pound; pound sign; hash; sharp;
crunch; hex; INTERCAL: mesh. Rare: grid; crosshatch;
octothorpe; flash; ITU-T: square, pig-pen; tictactoe;
scratchmark; thud; thump; splat.
The pronunciation of "#" as "pound" is common in the US but a
bad idea; Commonwealth Hackish has its own, rather more
apposite use of "pound sign" (confusingly, on British
keyboards the pound graphic happens to replace "#"; thus
Britishers sometimes call "#" on a US-ASCII keyboard "pound",
compounding the American error). The US usage derives from an
old-fashioned commercial practice of using a "#" suffix to tag
pound weights on bills of lading. The character is usually
pronounced "hash" outside the US.
The name "octothorpe" was made up by a Bell Labs supervisor,