I've always got a book with me. 
This is just a warning for everyone else.

These stickers are printed on durable, high opacity adhesive vinyl which makes them perfect for regular use, as well as for covering other stickers or paint. The high-quality vinyl ensures there are no bubbles when applying the stickers.

•  High opacity film that’s impossible to see through
•  Fast and easy bubble-free application
•  Durable vinyl
•  95µ density

Don't forget to clean the surface before applying the sticker.