@ has a well known meaning in Spanish, it is the symbol of "arroba" which is an old unit of weight, like a pound, ounce, etc. I still remember hearing on the local markets sellers pricing their goods for its arroba weight. In fact, when we read an email out load we do not say someone at somwhere dot com, we say someone arroba somewhere dot com.
It was commonly used in English in commercial correspondence, such as invoices, to separate a quantity from the unit price. I don't remember the exact notation, but it was something like 20#@$10 for "20 pounds at 10 dollars per pound." or "20@$10" for "20 items at 10 dollars each".
Anybody who can dig up an English-language B2B invoice from the 1950s or earlier?
