This is a Event Declined 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 12,900 icons, all in the same style and quality.
The icon's shaped like a square with a star at the center and a horizontal line that runs towards the top. At the top of the square are two vertical rectangles that overlap, one towards the left and one towards the right. At the bottom right of the square is a overlapping circle with a slanted line running through it.