Object.operator !=  

var target : Transform;
function Update () {
    // the target object does not refer to the same object as our transform
    if (target != transform) {
        print("Another object");            
    }
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public Transform target;
    void Update() {
        if (target != transform)
            print("Another object");
        
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public target as Transform

    def Update():
        if target != transform:
            print('Another object')