UCSICON system variable

Function Description:

The UCSICON system variable is used to control the visibility, location, appearance, and selectability of the UCS icon.
The coordinate system is different in paper space and model space. In the model space, user could switch between 2D and 3D style.

2D : if the UCS is the same as the WCS, the letter Z in UCS will replaced by the letter W. If rotating the UCS to make the Z axis on a plane that parallel to the observation plane (in             other word, the XY plane seems as a line for observer), the 2D UCS icon becomes a break sketch.
3D : if the current UCS is the same as WCS, looking down the UCS (the positive direction of Z axis), the origin in XY plane displays as a box; looking up the UCS, the box disappears.

Relative Glossary:

ON : Display the UCS icon.
OFF : Turn off the UCS icon.
ALL : Apply all changes on all active viewports. Otherwise, the UCSICON command only has influence on current viewport.
Noorigin : No matter where is the origin, the UCS icon displays at the left-bottom of viewport.
ORigin : No matter where is the origin, the UCS icon displays at the left-bottom of viewport.
Properties : Display the "UCS Icon" dialog box, users could control style, visibility, and position of UCS icon.