Quoted from MikeO:

It's a very subtle, yet satisfying, feature. You don't understand it until you have a good game and they start lighting up.

Quoted from I_P_D_B:

Yes, I ordered parts from them for several years. I bought my first and only NIB machine from them in 1979:
https://www.ipdb.org/showpic.pl?id=1823&picno=56454&zoom=2

(Correction from earlier. I bought Ice-Revue used from a local operator, not distributor. I didn't mean to imply it was new and unused.)
You're a little older than me. I bought my Cross Town in 1979. Dumb little story that goes with it. Years earlier, 1972 I believe, I was playing at an arcade in Cheyenne where I lived that had two woodrails among the many pinballs, one was Lightning Ball. I really like that game and as I played it with my friend, I exclaimed, "Why, I would pay A HUNDRED DOLLARS for this game!" Now, you have to understand the humble beginnings from which I sprang, so a hundred bucks was really saying something at that point in my youth. It was some astronomical number to me. Seven years later, with a good job, I got a call at work from someone who wasn't into pinball but knew I was, and who said, "Jay, the arcade is selling a lot of his pinball machines!" I barreled down there as soon as I got off work and saw both Lightning Ball and Cross Town for $150 each except the latter had a broken backglass. I was not fearful of that, and offered to buy his CT at $150 if I could also buy the LB for... a hundred bucks. He said yes! I soon found a CT backglass from a guy in Maryland, another little story but I'll stop talking. I still have both games. Little did I know years before that I would actually buy that Lightning Ball for a hundred bucks. I have to say, I like that story. I bought two other games along with them.
Now that I know you are looking for a Big Casino I bet I will think of you should I next see one, and since I am linked to this thread I can find you at that time.