Determining which direction an object will rotate?

There are plenty of rotation methods, but if I want to determine whether an object will rotate right or left in 2D space, how would I accomplish that?

virtual protected float GetRelativeAngle()
{
   // Get relative angle.
   Vector3 up2D = new Vector3(myModel.transform.up.x, myModel.transform.up.y, 0);
   float relativeAngle = Vector3.Angle(up2D, myModel.GetCurrentLookDirection().normalized);

   // Get relative sign.
   Vector3 relativeCross = Vector3.Cross(myModel.transform.up, myModel.GetCurrentLookDirection().normalized);
   if (relativeCross.z < 0) relativeAngle = -relativeAngle;

   return relativeAngle;
}
GetCurrentLookDirection is where the mouse cursor is pointing, by the way.

The problem is that sometimes I'm getting a positive relativeAngle when rotating my object either direction.

How would you approach calculating whether an object will rotate left or right in 2D space?