There is always tar from smoking on the other side of the touchscreen glass, it's disgusting when you clean it. I have cleaned no less than 20 touchscreens from various Bally Alpha monitors. When they are dirty, it looks like a white haze under the glass when viewed at an angle with the monitor off. With the game on, it is very difficult to tell it's there, so most people just leave it alone. My 044 lcd screen is relatively new, so it has very little smoke so I didn't take it apart to clean it as there is always a risk of damaging the touchscreen when you do so, they are very delicate.