While Cal's example is stretching the bounds, something like FORDMUSCLE is a trademark infringement. That's not to say it shouldn't exist, but by law it must pay Ford to use their trademark if Ford chooses to defend its trademark. That said, merely sending a cease and desist letter to a violator is demonstrating willingness to defend a trademark, and it can be used in future more flagrant violations to prove that you defend your trademark in all cases. It may sound semantic, but that is how the system works. If a company doesn't demonstrate a willingness to defend its trademark, it can be demonstrated that the TM has been watered down, and thus used against the company in future lawsuits. To prevent this they engage in idle threats.