Problem With Raycasthit Angle

I'm trying to create an AI that "sees" an object, and depending on the raycast angle, when the distance is lower than what I specified, the AI turns left or right...

I kind of did the job on getting the angle at wich my raycasthit hits an object... the problem is, it is always a positive value, never negetive... for example

This is my script:

 public Vector3 normal;
 public RaycastHit hit;
 public float _angleOfHit;

 // Use this for initialization
 void Start () {
 
 }

 void Raycaster(){
     Physics.Raycast (this.transform.position, this.transform.forward * 200000, out hit);
     Debug.DrawRay (this.transform.position, this.transform.forward * hit.distance, Color.red);
     _angleOfHit = Vector3.Angle (hit.normal, -this.transform.forward);
     }

 // Update is called once per frame
 void FixedUpdate () {
     Raycaster ();
 }