Using the Ohm Symbol
Ohm is the SI unit of electrical resistance, named after Georg Ohm, and its symbol is the capital Greek letter omega. A resistor marked 220 Ω passes one ampere at 220 volts; a 4.7 kΩ pull-up, a 1 MΩ input impedance and an 8 Ω speaker all use the same letter with a prefix. Because Ω is the last letter of the Greek alphabet, it also carries the meaning "the end" or "the ultimate", the alpha and omega of the Book of Revelation.
Which omega to use
Unicode has two characters that look identical: Ω, GREEK CAPITAL LETTER OMEGA (U+03A9), and Ω, OHM SIGN (U+2126). The second exists only for compatibility with old East Asian character sets, and the Unicode standard says plainly that the Greek letter is the preferred one for the unit. Normalisation converts the OHM SIGN into the letter, so text containing U+2126 may silently change when it passes through a database or a search index. The Mac shortcut Option + Z, the HTML entity Ω and every Greek keyboard produce U+03A9, which is what this page gives you. The mho ℧, an upside-down omega, once measured conductance; it was replaced by the siemens (S), and the symbol survives mainly on vintage meters.
Writing resistance values
Put a space between the number and the unit, and none between prefix and Ω: 470 Ω, 10 kΩ, 2.2 MΩ. Electronics schematics often drop the symbol and write 4k7 or 2M2, with the prefix letter standing in for the decimal point, because early plotters and BOM software could not print Ω. In running text, spell out "ohms" the first time if the audience is general. The lower-case ω is a different quantity entirely: angular frequency in radians per second.
Typing it
macOS has Option + Z. Windows has no Latin-1 Alt code, though the DOS-era Alt + 234 still gives Ω in many programs, and Word converts 03A9 to Ω after Alt + X. Neither phone keyboard has a long-press for it, so add the Greek keyboard on iPhone or Android and press Shift + V, or set a text replacement. In LaTeX, \Omega works in maths mode, and siunitx provides \ohm for units, as in \SI{4.7}{\kilo\ohm}. Pair it with the micro sign and the degree symbol when you need a full set of unit prefixes and signs.
Ω in culture and bios
Beyond electronics the letter is a badge of finality and mastery. Watchmakers, gaming clans and the "Omega" tier in ranking systems all use it, and in fiction it marks the last of a kind. On social media it turns up in bios as "Α to Ω", in gaming handles that want a Greek edge, and in the gothic fonts generator output, where its horseshoe shape fits blackletter styles. It reads as text on every platform, so it will not turn into a picture the way an emoji would, and it sits comfortably beside the delta symbol and a capital sigma in a physics-themed profile.