[QUOTE=Mahna Mahna]
In North America, most people seem to have no trouble identifying the pound key on a phone. It’s used all the time when navigating through automated phone systems like voicemail menus or teleconference logins.
I use it so often that the little design is starting to wear off the key. 
[/QUOTE]
It’s used all the time over here as well.
It’s called the hash key though. I’ve never heard it referred to as the pound key.
Pound=£ and a unit of weight.
If it’s in a prerecorded phone machine, then #, also known in Spanish as “la cucaracha” (the roach) or “el cuadradito” (the little square). Of course the pre-recorded messages never call it the roach.
I first encountered this in 2003 in the USA and had to ask a coworker what the heck was the machine talking about. That symbol isn’t used for anything in Spain, outside of telephone keypads and music sheets. I’d seen it before in the USA (1994-'8) but we called it “the number sign”.
And in any other context it’s either the squiggly crossed L used for UK currency, or a capital L used for prices in places in Spain which still use pounds for some items (the actual weight varies between 400g and 500g, not just by region but by - kind of item!)
Over here in Prague, when you add credit to the pre-paid SIMs, the instructional recording calls # “hash”.
[QUOTE=silenus]
Why “octothorpe?” There’s no “octo” anywhere near it.
[/QUOTE]
From the American Heritage Dictionary:
(Bolding mine)
And to answer the OP – of course it’s the ‘#’ key!
Incidentally, in Hebrew it’s called the “little ladder key”, which IMHO makes a lot more sense than any of the names mentioned in this thread.
‘Pound’ is a very US way of referring to the # key. Here in Canada, we always call # ‘number sign’, except in the context of phone menus. Many pre-recorded phone menus say ‘hit the pound key’. I think this is because either they are operating from the States or they were made in the States. I also suspect ‘pound’ provides a nice one-syllable counterpart to ‘star’ for *.
I have never, ever, seen anyone in Canada use # to indicate pounds weight.
Good lord, I’m starting to think I’m the crazy one. But there’s at least one other crazy person - whomever wrote this part of the wiki entry on “number sign”:
[QUOTE=Sunspace]
‘Pound’ is a very US way of referring to the # key. Here in Canada, we always call # ‘number sign’, except in the context of phone menus. Many pre-recorded phone menus say ‘hit the pound key’. I think this is because either they are operating from the States or they were made in the States. I also suspect ‘pound’ provides a nice one-syllable counterpart to ‘star’ for *.
I have never, ever, seen anyone in Canada use # to indicate pounds weight.
[/QUOTE]
Just another example of why, here in English Canada, we have to be bilingual: British and American. 
[QUOTE=Spoons]
Just another example of why, here in English Canada, we have to be bilingual: British and American.
[/QUOTE]
Make that ‘trilingual’. Imperial, US, and metric.
The hash key. I always hear my bank’s female electronic voice saying that from when I do phone banking. “Now enter your pin number, and press the hash key.”
My first awareness that it had another name came through stuff like MAD magazine and the like, I think.
[QUOTE=Lunar Saltlick]
Pound key actually seems to be used more and more often, contrary to what I think the OP is suggesting, but some people call it the number key, since it’s often used to designate a number: Number 4, No. 4, #4.
[/QUOTE]
“Number sign” is how I learned it, back before I could even type. On typewriters, it was included on the numerals line for the purpose of designating “numbers” as in “Incident #42783”. I didn’t hear it called “pound sign” until the advent of automated phone answering systems … back in the 1980s?