On Trigger Show Text

hey
I searched every where for it and used all of scripts… but it didn’t work. there is a trigger as you can see in scripts , I want to add a show.text order to it. I attached this script to my Trigger . what should I add?

using UnityEngine;
using System.Collections;

public class WarningArea : MonoBehaviour
{
void Update()
{

}

void OnTriggerEnter(Collider otherObjective)
{
    if (otherObjective.tag == "MainCamera")
    {
        audio.Play();
    }
}

}

If i am understanding you right, there are different approaches.
a) Use GUI.Label to show a text:

public class WarningArea : MonoBehaviour
{
    string message = "";
    void OnTriggerEnter(Collider otherObjective)
    {
        if (otherObjective.tag == "MainCamera")
        {
            audio.Play();
            message = "Warning text or something!";
        }
    }
    void OnTriggerExit(Collider other)
    {
        message = "";
    }
    void OnGUI()
    {
        GUI.Label(new Rect(0, 0, 200, 20), message);
    }
}

b) Use a TextMesh (GameObject → Create Other → 3D Text) and show it in OnCollisionEnter and hide it in OnCollisionExit

Hey Guy... It worked Perfectly... But the text was too small... I want exact Think With larger size... What Should I do?