3d Text shows through walls? How do I turn it on and off?

I am working with 3d Text in Unity, and ran into the problem that I put this text in a room, but as you go through the space you can see the 3d Text through the walls of the building.

My thought was then to trigger it on and off as you go through the door but thus far, I have been unsuccessful, causing the interactive to freeze when it is supposed to be triggered.

My two questions were whether there was a simple way to stop 3D Text from being visible through walls that I'm missing. Second, is whether there is something wrong with my script.

Here is my player Collision script below, attached to my player of course. Here is my new website where I have been displaying some of my demos, including this office space from "Lie To Me" where I am demoing this for a potential client. Currently the placard is a simple photoshop placard which breaks down, thus the need to make it 3d Text that goes on and off.

function OnTriggerEnter(hit : Collider) {

var TIM_ROTH_PLACARD : GameObject = GameObject.Find("TIM_ROTH_PLACARD");

if (hit.gameObject.tag == "TIM_ROTH_INFO" ) 
    Debug.Log ("IF HIT TIM_ROTH_INFO");

gameObject.FindWithTag("TIM_ROTH_PLACARD").active = true; 




Use this shader for the 3D text.