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 Material Design style
developed by Google. This style is based on extremely simplified shapes, thin two-pixel lines, and is optimized for 24x24 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 5,500 icons, all in the same style and quality.