how can i make appear an image when target is not found or lost?

Hi guys i want to bring up an image like a warning, for example “frame the target”, when the image target is not found or lost. How can i do this kind of thing?
thanks for your help

If you are looking for something that will show when something is not there anymore or is destroyed, I think this will be what you are looking for:

public SpriteRenderer notFound;
// This is for showing and hiding the not found message
public GameObject target;
//GameObject that you want to check if it is there

void Update{
if(target == null){
notFound.enabled = true;
} else
notFound.enabled = false;