(Incidently, the code charts for U+00AC (NOT SIGN) also say "= angled dash (in typography)." So I'm still a bit confused about in which discipline it is actually known as "not sign").
The not sign is often used in logical notation in Boolean algebra or sentential logic. See http://whatis.techtarget.com/definition/0,,sid9_gci843775,00.html
Other conventions are often used instead, especially use of the tilde. I believe, but could be mistaken, that use of tilde for "logical not" is older usage and that the specific "logical not" sign was introduced as a substitution because the tilde most often suggests approximation in mathematic use.
The not sign is used on the IBM mainframe platform in some computer languages, notably REXX. See http://www.ilook.fsnet.co.uk/rexx/rexcmdc5.htm
The backslash was also given the meaning "logical not" in REXX at some stage as an alternate in environments where the "logical not" sign was not available.
Versions of REXX adapted to ASCII generally replace the "logical not" sign by either ~ or ^ or allow either as well as recognizing the backslash.
See also http://www.uwm.edu/IMT/Computing/sasdoc8/sashtml/mindex/sc-index.htm for its use in another computer language.
Use of ^ meaning "logical not" generally derives from the use of "^" as a translation of the proper not sign in text files from EBCDIC to ASCII where the two symbols are normally equated. For example, from http://www.printek.com/products/autoforms.html
<< The following commands use the logical not ( ) sign or a caret (^). IBM terminals generally have the logical not sign. PC's running a terminal emulation program have a caret. In either case, both characters are a shift 6 on the keyboard. >>
Jim Allan
