it is whatever you get them to print.
if you get them to print it on self-adhesive vinyl... it will peel and stick.
really depends on what you plan on doing for finish. are you going to cover it with "plexiglas" or similar plastic? nothing? you can just get printed on simple card stock and just lay it under the overlay plastic with some double sided tape to keep it from shifting.
or get it printed on vinyl and apply it directly to the panel. be warned, with heavy use, the print will eventually wear through and show up as white spots where it gets constantly rubbed.... it should still be covered or those areas protected for long term use.