In some typefaces the "a" at the core of the glyph for "@" is similar to the italic glyph for "a". Examples include Bodoni, Bookman, New Century Schoolbook, Palatino, and Times, which are all serifed faces using a double-storey "a" in roman and a single-storey "a" in italics.
This is not so for many typefaces which have a double-storey "a" both in italics and roman, such as the sans serif faces Arial, Verdana, Gill Sans, and Univers. Despite the double-storey look of their italic "a", they still use a single-storey "a" inside the "@" sign.
In fact all the faces I've looked at use a single-storey "a" in the "@" sign. What faces, if any, use a double-storey "a" in that position?