There are many different classifications for Enso Circles based on the type and shape of the circle. Historically Enso Circles were drawn in black by Zen masters who often added a teaching, word or phrase of inspiration to their drawing. An Enso Circle without added words is referred to as a Mirror Enso.
As a person who is fond of contemplation, I especially like the term "Mirror Enso" as it poses a question to my mind. Is there another reason that a round empty circle is like a mirror? What can I see reflected there?
In 2012, I created a Mindful Brush installation for Naropa University's Graduate School of Contemplative Psychology. The artist statement read: "While it is said that an Enso Circle is a picture of the artist's mind at the moment that the circle is drawn, I think an Enso Circle is a mirror of the viewer's mind at the time that the circle is viewed." This is something you can look into for yourself.