You can have a veteran designation printed on your Idaho driver's license or state ID card as proof of military service. There is no charge when you get a new license or ID or renew one. Adding it at any other time costs a fee.
Go to any Idaho driver's license office, run by your county, and show official documentation of your honorable discharge. Ask for the designation when you apply for or renew your license or ID so it is free.
Official documentation that you received an honorable discharge from the U.S. Armed Forces, such as your DD214, plus your usual identity documents.