It's a logo for the words "Not Applicable". It is a box with rounded corners. Inside the box are the letters N and A. Both of them are capitalized.
This Not Applicable icon is a responsive icon. This means that it's optimized for four resolutions, from tiny 16x16 until highly detailed 80x80. The style comes from the latest Microsoft Office
, which makes it perfect for any Windows applications, in particular, those with ribbon toolbar control. Unlike other icon packs that have merely hundreds of icons, this monster icon pack contains 15,800 icons, all in the same style and quality.