Using the Trademark Symbol
The trademark sign signals that a word, phrase or logo is being used as a brand identifier, whether or not anyone has registered it. Any business can attach ™ to its own name from day one; no filing, fee or approval is needed. That freedom is exactly what separates it from ® on the registered symbol page, which may only appear once a trademark office has granted registration. Using ® without registration can be treated as a false claim; using ™ never can.
Placement and typography
The character is designed as a superscript, so never raise it again with formatting or it floats too high. Write it flush against the last letter of the mark: Nova™, not Nova ™. In longer documents the convention is to mark only the first or most prominent mention — a heading, a package front, a website header — and then leave the plain word alone. A page that decorates every occurrence looks like a legal filing and reads badly aloud.
™ or ℠?
Strictly, ™ is for goods and ℠ for services, so a bakery's cake brand takes ™ while its delivery service takes ℠. Outside the United States the service mark is almost unknown, and even American companies now use ™ for both, so you will rarely be wrong with the more familiar sign.
Copyright is a different thing
People often ask which of ©, ™ and ® to use on a logo. A logo can carry both a copyright, because it is an artwork, and a trademark, because it identifies a brand. In practice the ™ or ® goes beside the logo, and the copyright symbol goes in the footer with the year and owner.
The joke version
On social media ™ has a second life as sarcasm. Writing "having a Normal One™" or naming yourself "Certified Disaster™" frames an ordinary phrase as a corporate product, and the deadpan tone works because the sign is so associated with marketing. Discord display names, Twitter bios and Tumblr tags use it constantly, and it passes filters on almost every platform because it sits in the same font tables as ordinary punctuation. Pair it with a bold font brand-name style to push the parody further.
Where it can fail
The sign is in Windows-1252 and Mac Roman as well as Unicode, so it renders on essentially every device made this century. The only common problem is the fake version made from ᵀᴹ modifier letters, which some fonts draw at the wrong height and which search engines index as separate letters.