Open up Illustrator. Make a new document. The dimensions of the document don’t matter.
Under the Rectangle Tool, hold down the little triangle so that the options for the other shape tools pop out. To make the logo at left, I selected the rounded rectangle tool. But you could also select the Ellipse Tool. If you do, hold down the shift key to make the circle perfectly circular.
Drag out a circle on your new document.
You can fill the circle with any color you like. Set the stroke size to 20 px.
Next, go to the Control Bar, and select the Stroke Panel, or go to Window > Stroke. With the circle selected, click on the “Round Cap” option. Give the corner a “Round Join” and “Align Stroke to Center.”
Next, you will make the scallops!
Click on the “dashed line” option, set the dash to 0px, and the gap to 19 or 20 px about.
And there you go!