Brand refers to names, logos and slogans. For example, Nike is known for its slogan “Just do it” and swoosh logo. A trademark shows the origin and ownership of a product or service, which is used to protect names, logos, drawings, symbols and other characters related with a business. Coke？ and Coca-cola？ are registered trademarks of the Coca-Cola Company.
Many companies spend a lot of money and time registering their trademarks. There are at least two good reasons for this. Firstly, if you trademark a brand, you are the only person allowed to use that Brand name slogan etc. If others want to use that brand, they must ask your permission or pay some money. Secondly, registration also allows the owner to bring legal action against anyone who uses the trademark without authorization.
There are basic trademark symbols, e.g.“TM”for goods and“SM”for service.They tell the public that the product's name and design are the exclusive property of the company, but a registered trademark？ provides notice that it has indeed been registered.

According to the writer, it is not necessary for a company to register a trademark,

A trademark may be regarded as a protection for a brand name.

The trademark symbols TM and ? can be exchanged in a brand. 

Legal protection on a brand comes into force only after registration.