One example of an active effort to prevent the genericization of a trademark was that of the Lego Company, which printed in manuals in the 1970s and 1980s a req

One example of an active effort to prevent the genericization of a trademark was that of the Lego Company, which printed in manuals in the 1970s and 1980s a request to customers that they call the company's interlocking plastic building blocks "'Lego bricks', 'blocks' or 'toys', and not 'Legos'." Part of the reason they are being so picky about use of the name is to try to keep it from going generic. Unfortunately for them, I play with legos, my kids play with legos, and all of their friends play with legos...