When you select the rotation tool (W) you get a "Set: Rotation/Orientation" dropdown. This is the only way to change this setting that I'm aware of. An important setting that remains hidden most of the time.
When you have the select tool selected (v), and you select the "rotation" gizmo, no such dropdwon appears. It took me about 10 minutes to figure out where the rotation dropdown box was hiding becasue I selected the wrong rotation item in the toolbar.
Proposal: Rotation setting dropdown should appear in both instances.
If there are other ways to change this setting, please make it visible more often!