It is believed that "@" or the "at" sign originated from monks in the pre-printing press era as they were tasked with copying the Holy Scriptures tediously by hand, a "laborious process that encouraged typographical shorthand."
In 1536, "Francesco Lapi, a Florentine merchant, uses the @ symbol while penning a letter. It’s the first recorded use of the “at” sign outside a monastery."
More @ the New York Times.