[Aarongriffey]

My way......after sandblasting the plate, spray or roll the entire plate with the color the letters will be. You need to have at least three thick coats.
Next spray a medium coat of back ground color, the color the plate will be.
After it has dried well you have to rub off the last color from the numbers and letters, the raised stuff.
Now you know why you’ll want a lot (thick) paint on the letter n numbers and a thinner coat of background paint on them.
You can start exposing the letters by sanding them carefully with 400 wet r dry sand paper with plenty of water until the number color starts to show thru, then switch to rubbing compound and finally polishing compound.
If the plate has a raised line all the way around you can just mask off the rest of the plate with blue masking tape and spray the line with number color.
It is not a one evening job. It is one of the most frustrating jobs I know of. Very time consuming.
Better way is to use the silk screening process, but I don’t know how to do that.