It is a hexagon with rounded corners. Large rounded letters that say S T O P are centered both vertically and horizontally, putting them in the exact center of the hexagon.
This Stop Sign 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 5,700 icons, all in the same style and quality.