Back in my day, circa the 1950s, U. S. Girl Scout badges were 1 1/2" in diameter. Most of them had a green background and a green border, with colored embroidery for a design. Today, there's no need to limit ourselves. We can make our badges any size, shape, and color that we want. I chose purple for my writers' badges to represent purple prose.
To draw a badge we'll need something to make a circle (if we're making a circular badge); drawing tools; something to color the badge.