This is a correct answer to the following question about At sign. Yes or no?
Answer: Originally an accounting and commercial invoice abbreviation meaning "at the rate of" (e.g. 7 widgets @ $2 = $14), it was not included on the keyboard of the earliest commercially successful typewriters, but was on at least one 1889 model and the very successful Underwood models from the "Underwood No. 5" in 1900 onward.
Question: what is the @ sign called?
