The logo for Sigma pretty much looks like the letter E. The symbol has a deep bent in the middle towards the right and the middle ledge doesn't protrude as much as the top and bottom ledge.
This Sigma 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 6,000 icons, all in the same style and quality.