Protecting the intellectual property contained in a trademark doesn't just happen on the legal battlefield. It's also a battle in the minds of consumers. A company's goal is to use trademarked words and logos to capture the hearts of shoppers, but not to the extent that they will begin to use those words for products to which they don't apply.
Some brands are so well known that they enter the common lexicon, with potentially damaging consequences. If a brand name becomes used generically -- for example, Frisbee® for a flying disc, or Kleenex® for absorbent tissues -- that jeopardizes its continued use as a trademark. Velcro® has taken a humorous approach to protecting its trademarked word from genericide, reminding people to use the phrase "VELCRO® Brand hook and loop" instead, in this series of videos.
Examples of words that started out as trademarks, but then lost trademark significance, are escalator, zipper, and yo-yo. This shows that it is necessary to police the use of a mark, not just for trademark infringement, but also to make sure the public uses it properly.