When you use trademark protection for a name, logo, phrase, image, design or any combination of any of those things, you are declaring it your own intellectual property. A trademark is used to distinguish something as uniquely yours - or your company's - and is designed to protect that intellectual property from being used by other people or organizations. A corporate logo is one of the most commonly trademarked things; if another company even makes one that looks too similar to yours, they may be in violation of your trademark. The best way to seek damages in such an instance is by hiring an attorney who is well versed in trademark law.
When you register something with a trademark, you are explicitly forbidding other people and organizations from using it. Trademark infringement is a serious matter, as it can diminish the effect of your corporate image and might even tarnish it. Knowing your rights is critical. Having a trademark lawyer on your side can mean the difference between successfully pursuing a case and having it thrown out.
You should also keep these tidbits in mind: