On the planes that I need to stand out so I can see them I've found that red along with the yellow make the plane much more visible for my eyes. But as others have said, contrasting colors are going to be the most effective. Shapes and such will tend to disappear and blend into a general "blob" at distance so I don't like to rely on those for distinguishing between top and bottom. I prefer to do the top in one color and the bottom a contrasting color. But if you must do a shape or design to help tell the difference a basic stripe for the leading edge to the trailing edge will do more than most any other shape. Just make it a wide stripe so it can still be seen as stripe when the plane is away from you.

Hope this helps

Ken