TM, SM and the Circled R: What Each Symbol Means
TM is an abbreviated form of trademark. Service Mark is abbreviated as SM. A trademark is used for the name of a company, the name of a product, a logo and an advertising slogan, but a Service Mark is used for a service; you trademark or service-mark a service. It is the same thing, and the only difference is that a Service Mark is used only for services and anything concerning them.
What is the R in a circle? We use SM and TM when a trademark is not registered yet. When it is registered, you are expected to use a ® above the trademark. For example, Microsoft has a ® above its logo, which shows the logo is registered. Whenever you see ®, you should know that the logo or slogan in question has been officially registered as a trademark.
Wherever you see a TM or SM, that is, a brand name without ®, it simply means the brand is not officially registered yet. It is possible that such a brand is in the middle of the registration process. The company can claim that the mark belongs to them and that they are trying to officially make it their own. For example, Sokhan Corporation adds a TM at the end of the word Sokhan because the corporation aims to say: this name belongs to me and nobody else is using it.
Remember, though, that if someone actually owns a mark and you use it, the owner may sue you. First make sure nobody owns a mark, and then use it.