Doesn't have to go on a bumper, necessarily -- feel free to affix to your favorite (or least favorite?) Morlock!
 
(This item is a black sticker; if you'd like a white version, click back in the store and filter by Apparel to purchase the "Bumper Sticker [White]" item.)
 
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Here is what the manufacturer has to say:
Use indoors or outdoors with total peace of mind as each printable bumper sticker is made with thick vinyl material that has been laminated for top-tier durability against water, sunlight, and scratches.
Material: premium water-resistant vinyl
Waterproof sticky adhesive
Suitable for indoor and outdoor use
Easy peel backing
Matte finish
 
Here is sizing information from the manufacturer:
 
 
7.5" × 3.75"
Width, in
7.50
Length, in
3.75