ObjectLabel.cs

using UnityEngine;
using System.Collections;

[RequireComponent (typeof (GUIText))]
public class ObjectLabel : MonoBehaviour {

	public string npcName;
	public Transform target; // the object the label should follow
	public Vector3 offset = Vector3.up;    // Units in world space to offset; 1 unit above object by default
	public bool useMainCamera = true;   // Use the camera tagged MainCamera
	public Camera cameraToUse;   // Only use this if useMainCamera is false
	Camera cam;
	
	Transform thisTransform;
	
	// Use this for initialization
	void Start () {
		
		guiText.text = npcName;
		
	    thisTransform = transform;
		
   	 	if (useMainCamera)
       	 	cam = Camera.main;
    	else
        	cam = cameraToUse;
		
	}
	
	// Update is called once per frame
	void Update () {
    	thisTransform.position = cam.WorldToViewportPoint(target.position + offset);
	}
	
	
}