These characters have to be put on a brass curved piece of metal.
Oh, well that changes things
It looked like backlit plexi and I've done those overlays in the past using the method I described but obviously here the goal is different.
A mask / stencil sounds like a good option, and since they are small and detailed a laser would work very well if you select the right material. Use a non-vinyl material, such as a polyester (sometimes confusingly called polyester "vinyl" but it isn't a PVC material and much safer). Laser cutting most plastics releases toxic gases, some worse than others so venting or filtering is highly recommended.