PennDOT offers 53 distinctive registration plates honoring service members, veterans, retired service members and eligible family members. The plates the source describes in detail, including Medal of Honor, Purple Heart, Veteran and Gold Star Family, each have their own eligibility rules and application form.
Apply to PennDOT Driver and Vehicle Services using the application form for the specific plate you want, and include your proof of eligibility.
Proof of eligibility for the specific plate, which is usually your DD214, separation paperwork, retired ID card or casualty documentation.