Three symbols, one of which you may not use yet. Getting this wrong is a small mistake with consequences that are out of proportion to it.
TM: use it now
The TM symbol makes a claim: you are treating this word or logo as a trademark. It requires no registration, no application and no permission. You can put it on a name you started using this morning.
It has no formal legal effect of its own, which is not the same as having no effect. It signals that you regard the mark as yours, which matters to anyone deciding whether adoption of a similar name was innocent, and it makes clear to readers that the word is a brand rather than a description. If you are using a name commercially and have not registered it, this is the symbol you want.
SM: the same thing, for services
SM stands for service mark, and it does for services what TM does for goods. In practice most businesses use TM for everything and nobody minds. Use SM if you like the precision; it is not a distinction anyone will enforce against you.
R in a circle: only after registration
The R symbol means the mark is registered with the USPTO. Not applied for. Not pending. Registered, with a certificate and a registration number.
Using it before that point is a genuine problem rather than a technicality. If the USPTO sees the R symbol on a specimen for a mark that has not registered, it can refuse the application. Worse, a party opposing you can argue the false claim of registration was made in bad faith, and in some circumstances that can cost you rights you would otherwise have had. Courts have declined to enforce marks where the owner used the R symbol knowingly and without registration.
The other detail people miss: the R symbol is only good for the goods and services in the registration. If you registered for software and you are now selling branded mugs, the R symbol does not follow you onto the mugs.
Where to put it
Once, at the most prominent use on a page, usually the first or the largest. Repeating it after every instance reads as anxious and nobody requires it. Superscript is conventional. Neither placement nor size is a legal requirement.
What the symbols do not do
None of them creates rights. Rights come from use, and from registration where you have it. A symbol is notice of a claim, not the claim itself. Putting TM on a generic word does not make it protectable, and leaving the R symbol off a registered mark does not lose your registration, though it can limit the damages you recover, because certain remedies depend on the infringer having had notice.
The short version
- Using a name commercially and not registered: TM, today.
- Application pending: still TM. Pending is not registered.
- Certificate in hand: R, on the goods in the registration.
If you are not sure which stage you are at, the answer is TM, because it is never wrong.