It's a logo of Battle Net reduced to an image of a spiraling circle. The circle is enclosed by spirals. It pretty much looks like the same logo on the top of battle.net's website.
This Battle.net icon is made in flat color style
. This format was developed by Icons8 designer team and became immensely popular for use in web and mobile applications. Feel free to download this icon in PNG format for free, or unlock other formats for $5. Unlike other icon packs that have merely hundreds of icons, this monster icon pack contains 6,100 icons, all in the same style and quality.