If you got approved for SSI income, whether your disability is visible or not (your disability is nobody's fucking business. I will disclose mine. I'm autistic and Black and gay.) that's proof enough, and doctors can't deny signing your placard application. I was denied a placard, despite proof, but I'm in the final stages of getting approved for SSI, which I think legally, you can't be denied a placard after that proof. It comes down to a personal thing at that point. Many people qualify for a placard, but refuse to get a placard, and don't want one, for reasons that shall remain their own. So yeah. Thank you. :)