Number sign

[3] The symbol has historically been used for a wide range of purposes including the designation of an ordinal number and as a ligatured abbreviation for pounds avoirdupois – having been derived from the now-rare ℔.

[11] The instruction manual of the Blickensderfer model 5 typewriter (c. 1896) appears to refer to the symbol as the "number mark".

[16] The term hash sign is found in South African writings from the late 1960s[17] and from other non-North-American sources in the 1970s.

[citation needed] For mechanical devices, the symbol appeared on the keyboard of the Remington Standard typewriter (c. 1886).

[18] It appeared in many of the early teleprinter codes and from there was copied to ASCII, which made it available on computers and thus caused many more uses to be found for the character.

It was adopted for use within internet relay chat (IRC) networks circa 1988 to label groups and topics.

[19] This usage inspired Chris Messina to propose a similar system to be used on Twitter to tag topics of interest on the microblogging network;[20][21] this became known as a hashtag.

[45] Many early computer and teleprinter codes (such as BS 4730 (the UK national variant of the ISO/IEC 646 character set) substituted "£" for "#" to make the British versions, thus it was common for the same binary code to display as # on US equipment and £ on British equipment ("$" was not substituted to avoid confusing dollars and pounds in financial communications).