[GreenKeys] Why has the '#' symbol been called a number sign, pound sign, and now 'hashtag'?

[kn7sfz]

So, as I understand it, society is evolving to the point that your next 
phone call that is answered by a computer:

"Your call is very important to us and our menu has changed, so listen 
carefully to the following options:"

And one of the options was entering your information followed by the 
'pound' sign.

Are they soon gonna say 'followed by the hashtag sign' so the 
millennials and Gen-Z will know what to do?

Shudder...

de Richard kn7sfz