Levels and grids, like virtually everything else in the model are parametric elements and will appear in any view cut 90 degrees to the plane they define (confused? Look for another post in the future on this). Sometimes depending on the crop properties of the view you may want to define the position of these elements independently from where they are shown by default when you create the view.
When the '3D' symbol shows, that means the position of the grid bubble (or level, or section, etc) will be adjusted in all similar views to match where you place it. If you want to define the position of the bubble in only your current view, then click on the symbol and it will change to '2D' which means you can adjust it independently in your view and not affect its position in any other view. This will probably be most noticeable in elevations when defining the position of structural grids and levels.
If you move the bubble, and look at a different view and it moved and you ask yourself "What the...", then check the '2D' or '3D' property of that grid.
