In a DNS record, the at sign (@) identifies the domain being referenced. See DNS records
The at sign (@) has become widely identified around the world due to its use in Internet email addresses and Twitter names. Officially called an "asperand," the at sign separates the recipient's name from the domain name in email; for example, firstname.lastname@example.org.
A Twitter Symbol
The at sign is a prefix to a member's name on Twitter; for example, @BarackObama is President Obama's Twitter name. See Internet address