good idea. i wouldn't touch the car, but i wouldn't touch it anyway even without seeing a sign. I respect peoples' property and just look. I understand it as it's not ok to touch cars at car shows, in general. One of those unspoken rules. I don't understand why people feel the need to touch, fiddle with, or lean on them. There will be a few jerks though that will touch it just to piss you off if they see that sign.
After getting bumped into from behind the other day I feel like putting a sign in the back that says "slow moving vehicle STAY BACK"! or just "STAY BACK"!. something... lol. after that i was watching my mirrors and seeing how close people get, and i couldn't believe how close some of them follow or how close they pull up to me at a red light. makes me so mad. grrr. wish my car had something in the back that would pop out and punch them if they got within so much distance