haha-I cheated...:About 4,000 years ago was used as a writing sign in Elam at the Persian Gulf. Some thousands of years later it was adopted by the alchemists and given the meaning lead. But the metal was usually represented with the sign for Saturn,.

In alchemy was sometimes used also for spiritus, alcohol.

In music it signifies an instruction to raise a half tone, written before a note. See in Group 51.

The pharmacists of former times used to draw it on prescriptions, where it meant Take in God's name, and often was followed by . The basic meaning was, May this be good for you. This invocation cross, and sometimes , was followed by the name of the drug and the prescribed dose.

The is also used as a sign in the description of games of chess meaning checks, takes, or moves to.

In mathematics it can mean creates a completely ordered field. As a geometrical sign means equal to and parallel.

There is a stylized asymmetrical version, , often used on different types of paper forms. When is followed by a number the sign is short for number. The most up-to-date use of is on telephones, where it appears on a button. With this, and with another button marked , the telephone can be programmed in the so called AXE-system in various ways. After dialling a special number code the button with on it is used for end of programming. Before dialling such a code it means termination of the function represented by the code dialled.

But I'm not exactly sure what answer you're looking for, so interested to know!

...But I'm not exactly sure what answer you're looking for, so interested to know!

According to something I read today, the symbol has a name (like "tilde" for ~ or "asterisk" for *). That's what I was referring to.

Since several days have gone by and no one else has made a guess, I suppose I'll have to go ahead and tell you the name:

The symbol # is called an Octothorpe. At least according to the web site I saw.

In the UK we call it a hash or hash mark.

I've heard that term used in the US too but less commonly than "pound" symbol.