Recently an AutoCAD for Mac customer asked what are the small symbols next to a selected object that looked like this:
Starting in AutoCAD 2011 for both Windows and Mac, geometric constraints have become available to speed the creation of geometry by controlling relationships such as perpendicularity, parallelism, etc.
Any line or polyline that has had a geometric constraint applied will show the small flag next to the cursor when the object is selected to indicate the presence of the constraint.
Also, when the default option to 'Show All Geometric Constraints' is on, the symbols indicating the type of constraint applied will be displayed, as shown in the image above.
But, on a typical complex drawing, the constraint symbols can get in the way as shown here.
For the Windows version of AutoCAD, you can access the Parametric ribbon tab, Geometric panel and click on Hide All. With MENUBAR set to 1, the Parametric menu pull down appears with the same options as in the AutoCAD for Mac version.
For more on the use and benefits of geometric constraints, see the videos in the Help files.