How can i stop animation clip from being playing ?

I’m using Animator to play the animation clip.
I created two states. Animation_Sign and Animation_Idle.

The problem is in the script the switching between the cameras is working but the part to stop the animation clip is not working.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class AnimationCamera : MonoBehaviour
{
    public Camera animationCamera;
    public Camera mainCamera;
    Animator _anim;

    private void Start()
    {
        animationCamera.enabled = false;
        mainCamera.enabled = true;
        _anim = GetComponent<Animator>();
    }

    private void Update()
    {
        if (Input.GetKeyDown(KeyCode.C))
        {
            animationCamera.enabled = !animationCamera.enabled;
            mainCamera.enabled = !mainCamera.enabled;

            if (animationCamera == true)
            {
                _anim.CrossFade("Animation_Sign", 0);
            }
            else
            {
                _anim.CrossFade("Animation_Idle", 0);
            }
        }
    }
}

I used a break point each time it’s getting to the line:

if (animationCamera == true)

animationCamera is true. It’s never false.

What i want to do is when i switch to the animationCamera it will start playing the animation clip “Animation_Sign” and when i switch to the main camera stop the animation playing. and then again when switching start playing switching stop and so on.

you are checking animationCamera == true and it always return true because its component not bool so you need to check animationCamera.enabled and take decision, replace your update with the following code.

if (Input.GetKeyDown(KeyCode.C))
        {
            animationCamera.enabled = !animationCamera.enabled;
            mainCamera.enabled = !mainCamera.enabled;

            if (animationCamera.enabled)
            {
                 _anim.CrossFade("Animation_Sign", 0);
            }
            else
            {
                 _anim.CrossFade("Animation_Idle", 0);
            }
        }

this will solve your problem.