Section sign
On Windows, hold Alt and type 0167 or 21 on the number pad, then let go of Alt.
Copy it
About the section sign
Lawyers cite laws and contracts with it: § 3 means section 3, and a doubled §§ covers several sections at once. The usual explanation reads it as two letter s’s stacked one above the other, standing for signum sectionis.
German speakers call it the paragraph sign, and German keyboards give it a key of its own.