Dobry Kod PIN and other 80,800 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).
There is a retangled that is shorter than it is wide with four dots equally spaced in the the center of it. Below the rectangle is a circle that is about half the size of a the rectangle centered. Inside the circle is a check mark.