This is the Nagłówek 1 icon for Windows 10. Here we go. Optimized for 32x32 px, these are the simplest icons in the line style. Downloadable formats are PNG and SVG, among others. Icons8 icon pack is unique in providing a huge number of icons designed by the same team of four designers who create the new icons every working day in the same style and with the same quality. Same cool as the Bat Face, huh.
It is the letters "H1" in capital letters. The letters are only outlined, they are empty on the inside. The "H" looks like a normal capital H, and the "1" is the same height as the "H" with the top section pointed diagonally towards the "H".