Windows
Hold Alt and type 229 on the numeric keypad.
Greek
Copy the character, or use the shortcut that matches your keyboard and app.
Hold Alt and type 229 on the numeric keypad.
Character Viewer → sigma
Type 03C3 then Alt + X
Insert → Special characters → sigma
Click the keycap, then paste with Ctrl+V or Cmd+V.
Num Lock on, hold Alt, type 229, release Alt.
Use the Unicode, HTML, CSS, or JS value below in documents and stylesheets.
U+03C3σσ\03C3\u{03C3}Alt + 229