To help visualize the current orientation of the user coordinate system, you can display the user coordinate system icon. Several versions of this icon are available, and you can change its size, location, and color.
Use the command to choose between displaying the 2D or the 3D UCS icon. The shaded UCS icon is displayed when you open a drawing with a shaded 3D view that was created in AutoCAD. To indicate the origin and orientation of the UCS, you can display the UCS icon at the UCS origin point using the UCSICON command.
The UCS broken pencil icon replaces the 2D UCS icon when the viewing direction is in a plane parallel to the UCS XY plane. The broken pencil icon indicates that the edge of the XY plane is almost perpendicular to your viewing direction. This icon warns you not to use your pointing device to specify coordinates.
When you use the pointing device to locate a point, it's normally placed on the XY plane. If the UCS is rotated so that the Z axis lies in a plane parallel to the viewing plane—that is, if the XY plane is edge-on to the viewer—it may be difficult to visualize where the point will be located. In this case, the point will be located on a plane parallel to your viewing plane that also contains the UCS origin point. For example, if the viewing direction is along the X axis, coordinates specified with a pointing device will be located on the YZ plane, which contains the UCS origin point.