At sign

the key nobody needed

Unicode: U+0040 commercial at
Meaning: “At the rate of”, in accounting. Since 1971, also: this person, at this machine.
History: A merchant’s mark long before it was anything else, tied to the arroba — a Spanish and Portuguese unit of weight — and to the amphora as a unit of trade. It survived into the twentieth century as a little-used typewriter and keyboard character, which is precisely why it was available: when Ray Tomlinson needed a character to separate a user from a host machine in 1971, he wanted one that could not already occur in a name.
Variants: Wildly varied by typeface, since almost no one designed it with care until it mattered. Its names elsewhere describe the shape rather than the function: snail, monkey’s tail, elephant’s trunk, strudel, little dog.
Related: # the other character that found a second career online; & a ligature that became a name.
Appears: Every email address, every social handle, invoices and price lists, and the permanent collection of the Museum of Modern Art.
Evolution: Accounting shorthand → nearly-obsolete keyboard survivor → the addressing operator of the internet → a way of speaking to someone in public.

Sources · 3

documented Ray Tomlinson’s selection of the character for network mail addressing at BBN, 1971 — chosen for being unused, which is the whole story.
documented The Museum of Modern Art’s acquisition of the character into its architecture and design collection, 2010.
traditional Giorgio Stabile’s reading of a 1536 Florentine letter by Francesco Lapi as using @ for amphora. The letter is real; the interpretation is a scholar’s argument, widely reported as settled fact.