What command for special letters like sign for Pi and Omega?

You can find a list of all the special characters in the Character Viewer located in your Applications folder. '''Easier:''' You'll need to enable a special menu bar icon by going to System Preferences > Keyboard, clicking on the Keyboard tab, and then toggling on Show Keyboard & Character Viewers in menu bar. After you do that, you'll have this fancy new icon in the upper-right of your screen '''Apple logo: Shift-Option-K '''