Mark Pilgrim: ...when it was proposed “as exclusively a tilde in USA to appease SHARE”. I can find no further reference as to what this acronym means. I'm pretty sure it stands for United States of America.
It makes perfect sense that SHARE (arguably the longest running computer user's group who's tagline, "It's not an acronym, it's what we do" codifies the organization's mission: sharing information and experience for the good of all. SHARE meets twice annually.) would have advocated the tilde in 1966. After all, the tilde was nestled between the lowercase "r" and lowercase "s" in the original version of EBCDIC. Of course, there were versions of EBCDIC before the original version of EBCDIC, but they had the foresight to leave a gap for this important character.
Update: it has been educational watching Mark's history of the tilda grow before my eyes. Makes me wonder, however, if I shouldn't have been posting Apache's SOAP interop information here lest some web proxy decides to block it.