Micro sign
On Windows, hold Alt and type 0181 or 230 on the number pad, then let go of Alt.
Copy it
About the micro sign
Scientists write µ for micro-, one millionth: a micrometre is µm and a microgram is µg. It looks exactly like the Greek letter mu, μ, and Unicode keeps the two apart only because older character sets, Latin-1 among them, already had a separate micro sign.