Octalthorp. Note that, in Britain the '#' sign is called 'hash' and isn't used as the number sign - we write 'No.' for number.
It is called number sign, pound sign, and hashtag. Another name for it is octothorpe.
An octothorpe is another name for the number sign, also the pound sign (#).
Another name for a theater sign is "marquee."
the "number symbol" ( You know 'item # 4.')
the addition sign
pound sign or hashtag
An ampersat is another name for the "at sign", @ .
polygon or stop sign
The square root sign is called a radical
the plus sign
times. as in number times number
Another name for the opposite of a number is Additive Inverse.