I designed this acrylic license plate cover to replace the one provided by my car dealership. Note that this one does not advertise the dealership and that you can add your own quote at the bottom (or anywhere, really, depending on the design of your plate). The engraved areas are rather subtle but there are many products (such as Rub-N-Buff wax) that may be applied to add colour.
There are many types of acrylic on the market so be sure to test a small area for cutting and engraving. I have found that 2+ passes with lower power works best on acrylics.
If you run the job too hot, you may end up with a mess of melted plastic on your grid/ honeycomb so dial down your power and if the first pass doesn't cut through, simply run it again.
When attaching the cover over your plate, do not over-tighten the screws; acrylic is strong but it may crack if placed under great stress.