Rick, unless that one has been a victum...
of reverse engineering, the next step in the manufacturing process is to pour molten plastic over it and letting the plastic harden. Of course a form is fitted around the core during this step, but once the plastic hardens, the raised surfaces remain exposed and everything else is covered. In this instance, a yellow resin (plastic) is used and the inserts, "$1" the letters of "Harrah's" and the fine line of the box around "Harrah's" remain exposed.
If this piece was a victum of reverse engineering, then all the plastic has been removed, probably by melting.
Jim