The at-sign, @, normally read alood as "at", an aa commonly cried the at seembol or commercial at, an less commonly a wide range o ither terms (sic as the strudel), is oreeginally an accoontin an commercial invyce abbreviation meanin "at a rate o" (e.g. 7 widgets @ £2 = £14).
It wis nae includit on the keybuird o the earliest commercially successfu typewriters, but wis on at least ane 1889 model an the very successfu Underwood models frae the "Underwood No. 5" in 1900 onward. It is nou universally includit on computer keybuirds. The merk is encodit at U+0040 @ Commercial AT (HTML