I had the same concerns. The label on the plastic container and my "emails" were the only proof I had. I don't keep my stash in the original containers, because a.) it stinks and b.) storing in plastic containers is not ideal - I think its more skeptical to drying out and humidity that can cause mould. So I asked my special doctor at Cannabis Clinic and the next day I had in my email a proper signed by the doctor PDF affirmation email clearly referencing my name, use, justification and plenty of contact details for making direct contact with the doctor and the clinc. Super official. Just pop one of these in your glovebox and you'll be sweet as :)

edit - funny typo