magnetize the bumper sticker — they sell magnet strips at hobby lobby or Walmart with adhesive on one side that you can put on bumper sticker—remove it when at locations where keying is a problem.
I had done that with a previous bumper sticker (Crane, Georgia 3rd). The problem is that the 1999 Buick Century does not have enough metal in the bumper to adhere. So, I used the back of the Trunk, which was barely magnetic enough. The problem is when I took the car through the car wash without taking off the magnet, I lost it. I have put the Trump sticker on the back glass (so as to not damage the cheap Maaco job) and so far, so good.