How do I get the current active camera?

I have a billboard texture and it obviously needs to face the camera, but because I have vehicles and such the camera changes and all of them are not tagged "MainCamera" for important reasons. I tried to do something like this but it didn't work. Script:

 using UnityEngine;
 using System.Collections;
 
 public class Billboard : MonoBehaviour
 {
     public Camera m_Camera;
 
     void Update()
     {
         m_Camera = Camera.current.GetComponent<Camera>();
     }
 
     //Orient the camera after all movement is completed this frame to avoid jittering
     void LateUpdate()
     {          
         transform.LookAt(transform.position + m_Camera.transform.rotation * Vector3.forward,
             m_Camera.transform.rotation * Vector3.up);
     }
 }