The circles appear on the Navigation Map at the medium zoom levels, when you click on a particular object. "No Map Contact Update" must be unchecked in the GamePlay Options menu.
Here's a Fletcher DD without Radar installed:
Visual range on the outside. Hydrophone next, then Sonar looking like a half pie.
Next to the destroyer is a Omaha CL with only a Visual sensor shown (it's a stock game ship):
The following plane images are of a Betty Bomber and its Visual range ring:
A Zero Fighter with its Visual range obscured to the rear of the aircraft:
