Object.operator !=

public static bool operator != (Object x, Object y);

Description

Compares if two objects refer to a different object.

using UnityEngine;

public class Example : MonoBehaviour
{
    Transform target;
    void Update()
    {
        // the target object does not refer to the same object as our transform
        if (target != transform)
        {
            print("Another object");
        }
    }
}