What cannot be registered as trademark?

Any mark that is identical or deceptively similar to an existing registered trademark, or a trademark for which the application for registration is already in process, such trademarks cannot be registered. Also, a mark that would likely cause deception or confusion, or that appears offensive may not be registered. Geographical names, common names, common trade words and common abbreviation are also not registrable. The names which are listed under “Prohibited marks” and “Well known marks” are not registrable.