Fold several paper towels in half and stack them on top of a level surface. Lay the Sharpie ink stain face down on the stack of paper towels.
Pour a small amount of rubbing alcohol in a plastic container. Dip the corner of a cloth or sponge in rubbing alcohol.
Blot the permanent marker stain vigorously with the damp cloth or sponge. Replace the soiled paper towels with clean ones when they become soiled.
Keep blotting the stain until you have removed the ink. Hold the area of the jacket under cold running water to rinse the rubbing alcohol out of the fabric.
Launder the letterman jacket as instructed on its care and washing label.