Not allowed to ask you about your exemption, period. I just politely state " I have an exemption" and walk away. If they choose to invade my space and get nasty, we'll deal from that point. No one has yet done anything but grumble and walk away. Worst thing they can do to you is charge you with trespassing, there's no actual law to back up the mask paranoia. I don't even try to convince them or argue, you can't argue with stupid. Besides, most people are just looking for an argument, so they can get a "win" in their pathetic lives.