This is a Autograph 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 13,700 icons, all in the same style and quality.
Idea of Autograph Icon by Zee
We've received the idea on October 23, 2011 and created the icons on November 24, 2011