It is an icon for CLS. The capitol letters CLS are enclosed inside the middle of the box. The box is a four sided outline. It is a simple design.
This CLS 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.