Pound sign
On Windows, hold Alt and type 0163 or 156 on the number pad, then let go of Alt.
Copy it
About the pound sign
Under its curls, £ is a capital L for libra, the Roman unit of weight that gave the pound its name, and the bar across it marks an abbreviation. Old British money borrowed the same Latin: pounds, shillings and pence were written £sd, for librae, solidi and denarii.
Americans who say “pound sign” usually mean the number sign, #.