There are plenty of ways to get quantities of your own waterproof bumper stickers online or at the printer. But perhaps you want to test one out first before investing. If you want just one, and you want to make it at home, the process can actually be a little more complicated. It can be done, however, with an inkjet or laser printer or some free-hand art if you don't have a computer.
Practice first with regular copy paper. Copy paper is 8 ½ by 11 inches, standard bumper stickers are 3 by 11 inches and window stickers are 5 by 5. Type the words in black bold letters, insert any copyright or royalty-free graphics and set your copier to print in the horizontal format if you're making a bumper sticker to be 11 inches long. Or, practice hand lettering and drawing on the copy paper, at least in pencil, before trying it on the sticker paper.
Type and print out or hand-letter words on vinyl sticker paper once you've practiced and know you have the sizing right. Vinyl sticker paper is available at craft stores, art paper stores and online. Though it comes in boxes of 10 sheets, some stores may sell it in single sheets or offer a single one-time copy service using this bumper sticker paper after you've designed the sticker at home.
Trim to size (a paper cutter works best).
Apply protective spray coating, such as Preserve Your Memories, after the printout or art is dry. This prevents ink or paint residue from running in wet weather.
Adhere the bumper sticker to your car.