All you need is a black box with a hole in the front, the dot at the back of the box will scatter to much for any noticeable light to reflect out. now the only things that you can shine the dot and not notice it is glass and a lit frosted light bulb lol
My beam dump isn't quite enough for you from what I can tell. I just wanted to have the dot be controlled so that the .5W green didnt burn my wall and no one passing by would have to see the dot directly. If you want something that makes the dot much less visible, then you will need pretty much what a few others have said. Depening on power level I would get a box thats black inside and use some kind of diffusing reflector at an angle to reflect away from the opening. The quarter idea would probably work quite well.