Residue

I've got this little petpeeve about sticky things on the windowshield of cars I drive. I don't like them. I had a parking sticker thing in college, and it took me forever to get all that sticky residue off the windshield. Well, last school year at Emma's preschool I was required to have one of those sticky things on the windowshield of our car. Without it we would not be allowed to enter. So, I had no choice. But I DID have a choice on how much sticky I'd allow on the windshield. I had a brainchild. Instead of peeling the back off the sticky thing, I took some packaging tape from the house. I placed packaging tape on the back of the sticker and then applied it to the windshield. I figured once the school year was over it would peel right off and I'd have no sticky residue to mess with. So, here's a picture of our windshield now that I took the packaging tape off the windshield. Notice the nice clear square where the sticky thing would've been. Any suggestions?