I use this to find my car in large parking lots. Clips on easily and closes up nicely in the window. I keep it on the dashboard to remember to use it. It's not meant to be left in the window while driving. Something about not to exceed 25mph. But it's so easy to pop on and remove, that doesn't matter. I did have to mark "inside" and "outside" on the little white clip to put it on correctly. I chose red, because I thought the green one would blend in with trees and such. However, the flag can be changed, decorated, or any number of fun things can be done. I could probably attach a battery operated flashing light to it. The mind boggles at the endless possibilities.