This is a Monday 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.
A square with the Capital letter M lower case O inside of it. On top of the square is a smashed rectangle that has 2 vertical tiny rectangle coming out of the top. Similar to what a desk flip calendar would be