The first thing you should usually do to trademark a logo is perform a trademark search to ensure no other business is already using that logo. You can then begin to trademark the logo by using it for your business, typically in advertisements or on packaging for your merchandise. Although you do not necessarily have to register your trademark in order to trademark a logo, you should consider registration to ensure greater legal protection of your mark.
To trademark a logo, begin by doing a trademark search for a similar or identical logo. In general, a trademark will only protect a company name, logo, phrase, or other feature with respect to other businesses in the same field. This means that if your company manufactures golf balls, then you would want to avoid any logo that is already used by a sporting goods manufacturer, especially one that makes golf balls. You could potentially trademark a logo that is similar to one used by a software developer, in this situation, but you should avoid any logo that is too similar to one already well established in the public eye in order to avoid confusion.
Once you are sure that no similar business already has the logo you wish to use, you can then trademark a logo by using it for your business. This establishes your use of the logo, and effectively creates the trademark for it. You may want to register your trademark, however, for greater legal protection and to ensure that others know you have trademarked that particular logo.
To trademark a logo officially through registration, you will need to follow whatever procedures are required in your country. This will often involve filling out paperwork indicating your name and business, providing an image of the logo, a sample of the logo in use, and an indicator of what type of business you operate. You may also need to indicate whether the logo is already in use or if you intend to use it, as well as the specific type of products or services with which the logo will be used.
When you file the paperwork to trademark your logo, you will likely need to pay a filing fee as well. The process of registration may take some time, but your protection of the logo under trademark typically extends to the point at which you created the logo. You can usually perform a trademark search and register to trademark a logo with the appropriate government agency in your country, such as the Intellectual Property Office in the UK or the US Patent and Trademark Office.