Railroaders place to shoot the shit.

That little thing is this:The at sign (@), also called the ampersat, apetail, arroba, atmark, acosta, at symbol, commercial at, curlat or monkey tail, is formally an abbreviation of the accounting and commercial invoice term "at the rate of" (e.g. 7 widgets @ $2 = $14). In recent years, its meaning has changed to also mean "at" in the sense of "located at", especially in email addresses.

The @ has also been used as a prefix to usernames (e.g. @username) on social websites, simply as: (a) a textual addition to direct their attention; (b) denote an attribution or link, as on forums and suchlike; or (c) used so that the site's parser will detect and notify the person using that username of the reference on websites such as Twitter and Facebook (although parsing now automatically detects usernames without the symbol).

The Underwood Typewriter Company included the symbol on the keyboard of "Underwood No. 5" in 1900, and it was included on subsequent typewriters and their successors' keyboards.

Got that? Good! More grammar/vocabulary lessons headed ta your nabe, soon!