Canon EOS 5D MARK III Instruction Manual page 15

Custom Function Settings*
C.Fn2: Disp'lOperation
When any of the following functions are set, the <(_> icon can be
displayed on the viewfinder's bottom right (p.23).
Select the function for which you want the warning icon to appear, press
<C)> to append a <,7>, then select [OK].
When monochrome _ is set
If the Picture Style is set to [Monochrome] (p.131), the warning icon will
appear.
When WB is corrected
If white balance correction (p.140) is set, the warning icon will appear.
When one-touch image quality is set
If you change the image-recording quality with the one-touch image
quality function (p.328), the warning icon will appear.
When _SO expansion is used
If the ISO speed is set manually to L (50), H1 (51200), or H2 (102400)
(p.125), the warning icon will appear.
When spot metering is set
If the metering mode is set to [Spot metering] (p.168), the warning icon
will appear.
When the aspect ratio for Live View shooting is set to [4:3], [16:9], or [1:1]
(p.204), you can set the display method for the shooting area.
D Masked
[]_] Outlined
318