What Can and Cannot Be Registered as a Trademark
You can trademark the corporation name, the corporation logo, the product name and your advertising slogan. If you trademark each of these four items, no other corporation or person will be able to exploit it. If you have a special packing design, you can use the trademark for it too. However, the corporation name and the product name are usually the most applicable types of Trade Name.
The list of forbidden items is long and lawyers know them better than just anybody. However, there are some notes to consider. You can't trademark a proper noun. For example, John Brothers Company can't trademark the name John Brothers because it is a proper noun, meaning anyone else could bear such a name.
Another item is common nouns with a general meaning. I have a company named Doctor Advertise, which is an advertising company. When we were registering this trademark, we faced some complicated issues. The word Advertise is a common noun. Registration of this word and other 100% common nouns isn't allowed. Someone had tried to register the word tea, which is not possible. Even more complicated, you are not allowed to register a name which 100% indicates what you are going to do.
Language is another aspect to consider. If you want to register a trademark in the US and you decide to give it in Farsi letters, it's not going to be an easy process. Micro and Soft both have separate meanings, but the word Microsoft is recorded as a single word and even this one has its own meaning.
Names of geographical locations can't be used in a trademark, famous or unfamiliar. You can't use a flag design in your logo under any circumstances, and elements of the United Nations and other pertinent organizations can't be entered in the symbols you want to register.