In order to prove that you are disabled, there are some certificates required. This certification should only be given by the government and no one else. There is a miscellaneous certification form which needs to be filled out. Under this form, there is a disabled veteran certification which must be signed upon in the form. After this form is completed, you need to show your medical records for background check and inquiry.
Sometimes, they also require a current registration card or identification card as well. Once this whole process is complete, you can get the tag easily and show it to the organizations you are applying to.