Answer: No. Companies that produce stickers or charms that claim to block electromagnetic fields (EMF) are simply playing upon the ignorance of the average person with regard to their understanding of basic principles of physics.
It is not physically possible for a small device or multilayered metal sticker to effectively shield you from EMF while using your cell phone or laptop. Physics just does not work that way.
Any positive benefits users report are the results of a placebo effect, where the user is convinced that they are receiving benefit, have a more positive outlook, and generally feel better about their use of electronic devices. There is no scientific evidence that any of these stickers produce any effect at all.
A few companies which use sandwiched layers of silver, gold, or rare earth metals claim that their devices “remodulate” EMF emissions to transform them into less harmful forms of radiation. These claims, however, cannot be verified by standard physical tests and are more akin to homeopathic solutions that do not induce any known physiological mechanisms.