This is a System Report icon. We've made it in iOS style, first introduced in iOS version 7 and supported in all later releases up until now (at least iOS 11). This style is based on thin two-pixel lines and is optimized for 50x50 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 12,500 icons, all in the same style and quality.
This is a picture of a computer monitor. It is one big square with a smaller rectangle in the middle which has an exclamation point inside of it. There is a dot on the bottom right for the power button.