Buy a couple of blank magnetic bumper stickers for a few bucks on Ebay. [Nobody wants to put a real sticker on their car's paint job. You don't have to.]
Create something like this on MS Paint or any other similar program. Print it on a sheet of regular paper. Make 2 on one sheet of paper. Cut it out, just smaller than your magnetic bumper sticker.
Use clear packing tape, starting at the bottom, and overlap 3 strips of tape.
Use enough tape to wrap around the back and over the top, this will make your homemade magnetic bumper sticker rain-proof.
Put on a new message anytime you feel like it.
You can also buy pre-made bumper stickers on E-bay etc, and put them on your own magnet bumper stickers, but if you want to make your own, on the spur of the moment, this is how.
I’ve made quite a few yards signs. On some, I cover the Trump and Pence lines with dark blue tape, and put adhesive letters reading “LET’S GO” on the top space, and “BRANDON !!!” on the bottom space. I then spray clear adhesive on the letters and tape. On others,I cover “Pence” with blue tape, and put “WON BIGLY!” on one side and “ WON BY A LOT! “ on the other side. The libs here are melting down about my trolling.
No, don’t bother buying “magnetic bumper stickers”.
But rolls of magnetic sheet. Cut to fit whatever sticker you need. They can be had at hobby stores.