Display your letterman jacket in a shadow box -- a frame for three dimensional items. Purchase a shadow box large enough to accommodate your jacket or make your own using wood and glass. Mount the jacket within the shadow box using long pins stuck into a foam backing. Place the pins in a section that will be hidden from view, such as a sleeve's interior.
Place the letterman jacket onto a mannequin for a three dimensional view of the piece of clothing. You could either use a full body mannequin or just a torso, which the whole jacket will cover. Stand the mannequin upright. If the mannequin has no arms, stuff with crumbled pieces of packing paper so they'll stick out to show the emblems on the sleeves.
Create a hanging display for the letterman jacket. Attach two eyehooks to the ceiling. Attach two equal pieces of wire to the eyehooks. Tie the ends of the wire to a dowel. Slip the sleeves of the jacket over the dowel so it drapes over it like a hanger.
Mount the letterman jacket directly to the wall. Hang two hooks at the width of the jacket's shoulders. Drape the jacket over the hooks so it's spread out. Stick pins through the sleeve's interiors directly into the wallboard in the position you want them to appear.