I have a Remington 1100, and I like it. For trap, I leave a a small shell catcher attached so that I don't hit the guy to my right. It's a small clip that keeps the empty hulls from exiting the gun.
Common sense dictates that if you keep hitting your trap team member on your right every week, eventually he'll have something to say about it. It's common sense that it's not the proper thing to do.
When it comes to mention of not seeing a sign forbidding autoloaders without shell catchers when shooting with others, I suppose that I'd compare it to spitting sunflower seeds on someone's shoes. We all know that a sign isn't needed to tell you that it isn't right. Common sense is all that's needed.