Metonymy has to happen before a trademarked name is genericized. Consumers take a top-of-mind example of a product and use it to refer to all similar products in the category. And metonymy is not limited to trademarked names. Consider the use of the term "Nazi," a generic form of "Nazi," a member of the German fascist party under Adolf Hitler. Webster's dictionary provides this definition for "Nazi": "one who is likened to a German Nazi: a harshly domineering, dictatorial, or intolerant person." This process of likening is metonymy at work.
It's human nature to make things simple. We use brand names as generic nouns because it's easier that way. So what can you do to prevent your brand name from becoming generic? Unfortunately, it's not just a matter of making up a word. "Zipper," a name invented by the B. F. Goodrich Company for rubber overshoes, became associated with the shoes' closures, and the trademark acquired generic status.
Here's what you can do to keep brand name from becoming generic:
Using a generic descriptor: By pairing your trademarked name with a descriptive phrase, you can prevent it from becoming a generic noun. Consider "Jell-O® brand gelatin," where "brand gelatin" clearly differentiates name and generic term. By using this entire phrase consistently, Kraft Foods is able to prevent "Jell-O" from becoming genericized, at least in the legal sense.
Create usage standards: Establish guidelines for how your brand name is used, including where and how often its trademark designation (TM or ®) appears. This elevates its status in the minds of internal and external audiences and establishes a legal precedent of ownership. And never, ever use your trademarked name as a generic noun or verb. Even making it plural or possessive presents a risk.
Extend the meaning: This might seem counterintuitive, but the more different types of products a brand name represents, the less likely it is to become a generic term. Band-Aid did this by expanding its product family to include foot care products and antiseptic washes. Now the brand name Band-Aid represents more than just adhesive bandages. It is a brand standard within a category.
Reinforce the general term: When the brand name Xerox was becoming a generic noun ("make a Xerox") and verb ("please Xerox this document"), the Xerox Corporation launched an ongoing media campaign to reclaim their name and reinforce the general term "photocopy." (In spite of their best efforts, "Xerox" has entered the Oxford English Dictionary as a commonly used verb.)
More current examples are Google, which has begun discouraging publications from using the generic expression "google" to refer to any Web-based search.
Use it or lose it. As a trademark owner, you have to actively protect your trademarked name. That means using it consistently (according to the guidelines you've created) and protecting it against infringement. A trademark gains legal strength the more often it is used correctly in different contexts.
So the next time you leave a post-it reminding yourself to bring a thermos and your hacky sack on your camping trip, you're really leaving a sticky note about a vacuum flask and a footbag. And you'll understand the brand implications.