I don't like to make assumptions, because if I knew the game it would be easier.
If you are taking about the panel itself, and not speaker grills, these were molded into the panel at the factory for all late model Williams games starting around 1996 and chrome ink printed.
If you are skilled with silver chrome paint you can mask and spray.
Alternatively, you can sometimes buy a replacement panel either as a NOS or leftover.
If you referring to speakers (earlier games)...
Do you mean a reverse stencil?
They were factory painted as well.
The easiest way to restore the design is with a Testors red enamel paint pen and a steady hand.
If you want to be OCD, you can still find a few extras lying around, buy an old speaker panel, or create you one stencil with a pattern tracer, cut out with an exacto knife, take out the grill, and respray.
Any sticker you make from plastic laminate will look tacky.