A card, word, date, etc., chosen by a spectator magically appears as a hideous painful welt on the magician's forearm.
First, the magician must determine what the secret word, card, etc. is that the spectator selected. This is done through one of the standard means of information revelation (e.g., asking "If you were to say your word out loud, what would it sound like?")
Next, the magician casually puts a hand in a pocket where the Stigmata device is hidden. The Stigmata device is simply a set of metal plates embossed with common letters, numbers, and card symbols. The magician uses touch to select the plates appropriate to the revelation and inserts them into the Stigmataburner™, which uses electricity to heat them (an extension cord runs down the magician's pants leg).
When the plates are good and hot (about 90 seconds), the magician dons a flesh-colored potholder, removes the plates, and presses them briefly but firmly against the opposite forearm where they cause instant, painful, welt-raising, second-degree burns, much to the audience's amazement. While everyone is staring goggle-eyed at the display, the magician returns the potholder and hot plates to their pocket (which has been lined with asbestos) and the evidence is gone.
This trick, though effective, has a few drawbacks.
First, the welts are intensely painful and may take days to go away and can leave permanent scars.
Second, repeatedly abusing the skin in this horribly painful way can make one significantly more susceptible to skin cancer.
Third, one little slip and the intense heat from the pain-causing plates can make the magician's clothing catch fire.
And fourth, did we mention the horrible pain?