Tomlinson's final clever little hack was to use the @ sign to distinguish emails arriving from remote computers, so the format was "Tomlinson@remotemachine" (the .com and the like would be invented later). The choice was happenstance: as Tomlinson later told the Smithsonian, he'd been looking around for something to use when he noticed the @, poised above "P" on his Model 33 teletype terminal. "I was mostly looking for a symbol that wasn't used much…I could have used an equal sign, but that wouldn't have made much sense." That the @ key was even on the computer keyboard was itself rather by happenstance, too. Its origins are obscure (one theory suggests it is an "a" placed within an "e" and an abbreviation for "each at"); it was sometimes used in commerce to designate the price at which each unit was being sold.

Tim Wu, The Attention Merchants, loc. 645