I engraved it in down to the metal with a power drill. Definitely not a paint marker - my handwriting is neater than that!
I did take the eBay photos before putting in the marking - all of the 66es and other signs are so marked.
As the engraving is difficult to see in a photo, I am happy to show everyone these signs in person. See you at the Tucson AZ plate show this Saturday, and future license plate, gas/oil, and other automobilia shows in CA, NV, AZ, and maybe even further away from my home of San Diego.
