Here is a procedure that uses a common plastic toner type laser printer, regular paper, a small plastic laminator, and a kitchen freezer. You will also need powder coated sheet metal. I've been using aluminum flashing that is painted white on one side and tan on the other. The stuff cuts with scissors.
The toner from the printed artwork fuses to the powder coat because they are the same type of plastic. Just soak in water to remove the paper from the toner. The result is artwork that is difficult to remove with heavy rubbing with a 3M pad.
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Your questions and comments are welcome.