I haven't been able to find any information online from custom enclosure manufacturer websites or discussion websites such as this. I found a somewhat related thread in the 3dprinting Stack Exchange but it never led to any real conclusion on the generally accepted method of creating these LED effects (LED Indicators with 3D Printer).
Based on my observations of these physical products, my best guess is that they are using some type of translucent material, possibly tinted acrylic, and using some method to print the negative symbol shape on the back side of the acrylic. Then a light pipe or direct LED lighting can be used to illuminate each symbol.
Could anyone confirm if this is the method that is used? If so does anyone have more details on specific materials, printing processes, and manufacturers which can provide this service?
Thank you all for your consideration.