The cards used by the sons and daughters of Oberon in Roger Zelazny's Chronicles of Amber for communication, transportation, and mischief. To have a trump for someone (or something) means you can speak with that person, travel to where they are, distract them with a contest of wills, and any number of interesting things.
Evidently, anyone can make a trump from any material (Dworkin drew one on the wall of a jail cell.) as long as they learn the trick and have some talent drawing or painting.