As some of you may already know, in order to type in special characters (like @, £, $, et cetera), you need to hold Ctrl and Alt. However, I tried several options in the Keyboard Layout and progressed nowhere. Holding Ctrl and Alt while pressing 2 so I can type @ does not work.
Ctrl+Alt+? is only used when the keyboard layout doesn't include an Alt-Gr key, as such it is supported by Windows for emulation purposes (as in: keeping the functionality across multiple layouts).
Using the Alt-Gr+? combination is standard and should be supported by your keyboard layout.
(In extension to my comment)