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In the book "Scientific Style and Format: The CSE Manual for Authors, Editors, and Publishers" it says:

The octothorp ("8 fields" ) has been used in cartography as a symbol for "village "... .

But, the octothorp, as a number sign, is used in the U.S. to signal an apartment or unit within the block at a particular address. For example:

Mr. M Murphey
72 President St #4

Is it possible that this use of the octothorp has its roots in its use in older cartography to mark the site of a village?

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Isn't it just that # is a symbol for "number"? Not sure how it evolved to that point, but that's basically why it's used to denote apartment units. –  Anna Lear May 31 '13 at 20:26
A theory claims that back in early 1900, the Teletype Corporation was the first to use # to mean "number". That Wikipedia article about the symbol uses the word hash 15 times, whereas it only uses octothorp 3 times (plus a few references to the alternative spellings octothorpe, octathorp, octatherp). Maybe this is a US/UK split, but I certainly wasn't aware the term octothorp was "well known". I know I wouldn't have got far on telephone IT support in the UK saying to someone "Now press the octothorp key". –  FumbleFingers May 31 '13 at 22:18
The use of # for a suite or apartment number is much older than the 12-button telephone keypad. Its placement, however, is not as shown in the OP. With us, the house or building number precedes the street name but the apartment follows. The slash/virgule is not used at all. Example: 72 President St #4 –  Andrew Lazarus Jun 21 '13 at 22:44
Carlo, it is used in addresses not because it is associated with addresses but is associated with numbers, and it turns out that apartments are labeled with numbers, that's all. Numbers came before apartments. See the wiki article on the number sign, which accords with my understanding. The wiktionary entry is speculative and deficient. –  Mitch Jun 22 '13 at 16:24
More here: languagelog.ldc.upenn.edu/nll/?p=2461 –  dotsamuelswan Feb 26 at 18:34

1 Answer 1

This sign is more usually called the pound sign, hash or number sign. According to some theories, the "pound sign" stemmed from a simplification of the abbreviation of lb to mean "pound":

Historically, the pound name derives from a series of abbreviations for pound, the unit of weight. At first "lb." was used; however, printers later designed a font containing a special symbol of an "lb" with a line through the verticals so that the lowercase letter "l" would not be mistaken for the numeral "1"....

Ultimately, the symbol was reduced for clarity as an overlay of two horizontal strokes "=" across two forward-slash-like strokes "//".

So according to this, the hash sign which came to mean "number" (as in, "a #2 pencil" would be spoken as "a number 2 pencil") developed separately from the use of a hash sign in cartography. Similarly, in reference to apartments, the use of a hash sign is simply shorthand. Thus, "apartment number 4" could be written as "apartment #4".

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I’ve never heard it called a “hash” in the States. –  tchrist Jun 22 '13 at 1:18
@tchrist: As in hashtag?! –  Andrew Lazarus Jun 22 '13 at 3:47
@tchrist, Some folks haven't heard of Twitter either... –  Pacerier Feb 24 at 7:22
"Pound Sign" is standard Telecomm lingo "Hash" is standard Comp-Sci lingo "Number Sign" is common in general Commerce –  H.R.Rambler Feb 27 at 18:56
Is there also a connexion between 'hash' and 'hatch' as in 'cross-hatching'? A hash-sign does look like an extract from a cross-hatched area on a map. –  David Garner Mar 1 at 17:01

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