There are a few ways to checker plastic gun grips. One is to use a black light. If the grips have been checker-plated with black light-sensitive material, they will glow under ultraviolet light. Another way to check for the presence of such a material is to scratch the surface of the grip with a sharp object; if it scratches easily and reveals a shiny surface underneath, then it has been checker-plated with luminescent material.
A third way to determine whether or not grips have been checker-plated is by their weight. Plastic gun grips that have been checker-plated will be significantly heavier than those that have not. This is because the checker-plating process adds a layer of material to the surface of the grip, which increases its weight.
Finally, you can also look for signs of wear on checker-plated gun grips. These grips will typically show more wear than those that have not been checker-plated, due to the added layer of material on the surface. If you see signs of wear, such as scratches or scuffs, the grips have likely been checker-plated.