About this character
U+2122 TRADE MARK SIGN is the small superscript "TM" used after a name or logo to claim it as a trademark. Unlike the registered trademark sign U+00AE ®, ™ does not require any official registration: under United States common-law trademark, anyone using a distinctive mark in commerce may attach ™ to it as a public claim. The encircled R, by contrast, may only be used for a mark that has been registered with the relevant national trademark office. In practice this means a startup can write WidgetForge™ from day one but cannot legally write WidgetForge® until the trademark office issues a registration certificate.
Unicode encodes ™ as a single codepoint in the Letterlike Symbols block because the symbol is so commonly typeset as a superscript that it warrants its own glyph for kerning and baseline-shift purposes. The Unicode standard records its compatibility decomposition as the superscript form of the two letters T and M, which means it will normalise to the plain ASCII string "TM" under NFKC and NFKD. For information about normalisation in general — and the cases where NFKC will strip your trademark sign and replace it with bare letters — see the normalization guide.
The HTML named entity ™ is older than the HTML 4 specification and works everywhere. The companion mark U+2120 ℠ SERVICE MARK exists for the same purpose applied to services rather than goods, though it is far less commonly used. U+2117 ℗ SOUND RECORDING COPYRIGHT is the equivalent for phonograms — the encircled P printed on physical records and CDs. The trade mark sign is occasionally confused with the visually similar combining diacritics or with the bare letters "TM" set in superscript by CSS; the encoded character is generally preferable because it survives plain-text contexts and copy-paste.
From the Unicode data
Its emoji name (CLDR short name) is “trade mark”, in the Symbols group, subgroup other-symbol. By default it is shown as a text glyph; follow it with U+FE0F VARIATION SELECTOR-16 to request the colour emoji form (U+2122 U+FE0F), or with U+FE0E VARIATION SELECTOR-15 to force text style.
It is a superscript form of U+0054 T + U+004D M (compatibility decomposition <super>). NFC and NFD leave it alone, but NFKC and NFKD replace it with U+0054 T + U+004D M. Search engines, identifier checks and username systems that apply NFKC will treat the two as the same text.
Its East Asian Width is Ambiguous: it takes one column in Western contexts and two in East Asian legacy contexts, a common cause of misaligned tables in terminals.