2.3.6 - Markings and Signs
Step Description:
1. On the Create Roundabout - Markings And Signs dialog box, set the desired options for the following settings:
- Signs
- Pavement markings
- Crosswalk markings

2. Click Finish to create the roundabout.
NOTE: Informational messages may be displayed to inform you of certain conditions. Click OK to close these messages.
The Finished Roundabout is created in the drawing.

AutoCAD Civil 3D 2012 User's Guide reference:
User's Guide - Dialog Box Reference - Intersections and Roundabouts Dialog Boxes - Create Roundabout - Markings and Signs Dialog Box
For more information watch the video below:
Create Roundabout (WMV)