ISO and other 86,700 icons from Icons8 icon pack follow the visual guidelines of the operating systems: Windows, iOS, Android KitKat, and Material. PNG format is free up to 100x100 px. Icons are availble for download in PNG and vector (SVG, PDF, EPS, and more).
The logo is a rounded rectangle that is longer horizontally than it is vertically. On the inside of the rectangle are the letters "ISO" in all capital letters. The letters are centered on the inside off the rounded rectangle.