A circular arrow requiring adaptations carry the same licence.
The SA mark requires that anything built on the work is released under the same licence. It is the condition that makes a licence copyleft: permission is granted on the condition that it is passed on.
Requires that any adaptation of the work is distributed under the same licence as the original.
This is the condition that makes a licence copyleft, and the reason a share-alike work cannot be folded into a more restrictively licensed one.
A circle outline containing an arrow bent round on itself into an almost closed loop, its head pointing back toward its own tail.
The copyleft C is a concept with no legal force of its own; the share-alike mark is a specific licence condition that does have one.
Both are built from circles.