High quality Reproduction 503rd Parachute Infantry Regiment pocket patch.
Pocket patches were applied to M41 jackets, jump jackets or flight jackets, usually on the left breast. However, this varied a bit from unit to unit- so if historical accuracy is important, it's best to research the specific unit. Machine-embroidered on twill or wool, or hand-sewn bullion.
You can sew this on anything you wish, but it is historically incorrect to wear these in the field or "in combat". Pocket patches were only for casual or "walk out" uniforms.