Mathf.Sign being ignored.

I have a cube rotating around its Y axis with deltaPosition controlling its speed. I’m trying to use Mathf.Sign to determine its rotation direction but it doesn’t seem to pick up the value, and the cube only rotate in one direction. Here’s my code:

void dragRotate ()
	{
		if (Input.touchCount > 0)
		{
			Vector3 touchDeltaPosition = Input.GetTouch (0).deltaPosition;

			if (touchDeltaPosition.x != 0)
				rotationSpeed = 10f;

			transform.Rotate (new Vector3 (0, rotationSpeed * Mathf.Sign (touchDeltaPosition.x) * Time.deltaTime, 0));
		}
	}

I’d really appreciate the help!

Found a stupid simple solution:

rotationSpeed = 10f * Mathf.Sign (touchDeltaPosition);

transform.Rotate (new Vector3 (0, rotationSpeed * Time.deltaTime, 0));