Preparation:

1. A texture file: .png format.
2. A .trfsign file: referenced  .trfsign files in installation directory (e.g C:\IPG\carmaker\win64-9.1\TrafficSigns).

Please make sure that the Texture file name in .trfsign file should be identical with the .png file.

Steps:

1. Create a new folder named TrafficSigns in your project folder, then create a country folder named USA under TrafficSigns folder.
2. Put the texture file and .trfsign file in it.
   
3. Open scenario editor, navigate to the scenario setting and then you can choose a Country under Localized setting, it should be the same to the country you have defined in your project folder (here it should be USA).
   
4. Then add a traffic sign to the road, you will find the traffic sign you just added.
   

For further information please take a look at the Appendix B - "Traffic Sign File Format" in the CarMaker Reference Manual.