What is this symbol? ⎋ (it is listed as menu shortcut) The shortcut the Apple menu reports for the Force Quit menu item is ⌥⌘⎋. (the last character is the one Unicode calls broken circle with northwest arrow.)

What key should I press to invoke the Force Quit menu item?
To be concise: the symbol you're asking about, the circle with the arrow escaping from it (that's the way I remember what it means), is the Apple way of saying 'The ESC Key'.

So the menu item ⌥⌘⎋ 
is option+command+esc pressed simultaneously.