Idea of High Priority Icon
There is a single diamond shape, and in the center of the diamond shape is an exclamation mark. There's no other detail to the sign or any other marking on it, it seems like a warning sign of a sort.
This High Priority 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 6,100 icons, all in the same style and quality.