I bought a set of these and they work flawlessly. Have used them at several car shoes and it allows people to really see the interior and as well works great to keep people from messing with the doors or trying to get into the car. Great product, great innovation.
Here is a pic of a friend's set and what he did with his. Great idea, I am making up a set of signs for myself.
I definitely recommend these.
See this post if you want to get a set;