According to Love to Know Cleaning, if a scorch mark on an iron is still fresh, unplug the iron and try to remove bits of the burned fabric from it using tweezers or chopsticks. Both fresh scorch marks and old scorch marks can be removed using salt, vinegar, laundry detergent, dish soap, hydrogen peroxide or metal polish.
To use salt to remove scorch marks from an iron, place several large tablespoons of table salt on a soft cloth. Place the cloth on a flat surface, and turn the iron on the cotton setting. When the iron heats up, place it on the salt, and rub it back and forth until the scorch marks disappear. Unplug the iron to allow it to cool down before wiping off the metal plate with a damp cloth.
Vinegar can be combined with the salt treatment for extremely hard-to-remove scorch marks. Mix a few teaspoons of salt or baking soda with hot vinegar. Stir the mixture until the salt or baking soda is completely dissolved. Soak a clean cloth in the mixture and wipe down the iron's metal plate. Keep wiping the scorch mark until it's gone. Wipe the iron off once again with a clean, damp cloth before putting it away.