Traffic Signs:
CarMaker offers a wide range of traffic signs as accessories for the scenery. You can make the scenery look more realistic and rebuild a road from the real world. But as you may have already noticed, the IPGDriver won't react on these traffic signs.
Nevertheless, Traffic Signs are not only available to beautify your scenery. You can use them for our Traffic Sign Sensor or to check your detection algorithm of a camera based ADAS system.

Markers:
If you want the IPGDriver to react on Traffic Signs, you have to use Markers instead. You can choose between several Marker as shown in the picture below. For Driver speed and Driver stop, you can hide the marker (which is also visualized as a sign) in the animation with the checkbox.

As you can see, with Markers you have more possibilities as with Traffic Signs. For instance, you can build a Pylon alley or trigger a Minimaneuver Command by using DrivMan command if the ego car passes a defined point during the simulation. In the end, it depends on the specific use case which functionality one should use.

Since CarMaker 9.0, you can use a new reworked concept for lane individual Markers. Along with this, Markers have a new design in the visualization and can't be mixed up with Traffic Signs anymore. For more information, have a look into CarMaker 9.0 User's Guide chapter 5.9.1 "Markers".