This is a Ok 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.
There is a check mark, which is placed in the middle of a larger circle. The check mark looks similar to a reversed L, and is slanted so that the point where the two lines of the L meet is the lowest point. It is a standard check mark.