It's a logo of Poster reduced to a sheet of paper. The sheet of paper is slightly bent on the bottom right hand side and has a hole on the top. It looks like a normal poster you would see on a bulletin board.
This is a Poster 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 13,900 icons, all in the same style and quality.