Those were furn times without a computer. It was a simple and fast process to make a sandblasted sign. After the glue-up and application of sandblast mask we would project the our image, using the overhead projectord and off we went for the sandblasting. I can tell by your photo's the person blasting these signs didn't have a large enough compressor. That's evident by the shallow blast. With 185CFM air supply the "latter Wood" is removed along with the hard wood grain. I always go down a 1/2" or more. It makes painting the letters with a roller much easier.
Although we rely on the router for out woodgrain, on PVC, it doesn't look nearly as good.