The Common Law of Passing Off can take action against a person for unauthorized use of an unregistered trademark without prior permission. A Passing Off can be sustainable only if:
The holder can prove his prior and continuous use of the unregistered mark
The holder has built up a reputation in the mark
The other person’s use of the mark has caused some sort of harm to the holder.
It is extremely difficult and expensive to prove a passing off action. It is easier to take legal action if the mark is registered. An action against infringement of trademark can be taken rather than using passing off if a mark is registered.
