GUIs for Power ups? No idea.

Hi, I'm having trouble with coding for a HUD. So, what I'm trying to do is make it so when a power up is picked up, it shows a little decal in the bottom right corner of the screen, and then, when you use the power up (by pressing the number that corresponds), the little decal goes away.

Here's the script that controls the powerups:

 var hasPowerup:boolean = false; //variable that checks if the player has picked up the powerup
 
 function Update()
 {
     transform.Rotate(Vector3.up * Time.deltaTime * 30); //slowly rotate the powerup object
     
     if(hasPowerup == true)
     {
         /*
         Activates GUI for power up, in bottom right
         */
         Debug.Log("Powerup Obtained");
         if(Input.GetKeyDown("1"))
         {
             Debug.Log("RATE!");
             Power();
             hasPowerup = false;
             /*
             Remove GUI for power up
             */
         }
     } 
 }
 
 function OnTriggerEnter(obtainPowerup : Collider) //Detects collision between the player and the powerup object, and sets hasPowerup to true
 {
     if(obtainPowerup.gameObject.tag == "Player")
     {
         hasPowerup = true;
         transform.position = Vector3(0,0,0);
     }
 }
 
 function Power()
 {
     Fire.rate = Fire.rate / 2; //Doubles the rate of fire
     Debug.Log("/2");
     yield WaitForSeconds(8); //Waits for 8 seconds
     Fire.rate = Fire.rate * 2; //Sets the rate of fire back to normal
     Debug.Log("*2");
 }

Kind of a long code... But yeah, how do I do this?