The symbol used to indicate an unregistered trademark is ™.
The ™ sign tells the public that a person or company is claiming a word, phrase, logo, or design as a trademark. It does not, by itself, prove that a government trademark office has approved or registered the mark. Businesses may use it while developing a brand or while an application is pending, depending on local practice.
The main mix-up is with ®, the registered-trademark symbol. ® is reserved for marks officially registered in a relevant jurisdiction, while ℠ is generally used for an unregistered service mark—something identifying services rather than physical goods. © is different again: it identifies copyright protection for creative works such as books, music, artwork, and software.
Trademark rights and symbol rules vary by country. In the United States, ™ can be used for goods and SM for services even without federal registration. Registration generally provides stronger, broader remedies than an unregistered claim, although unregistered marks can still acquire protection through use under applicable law.