Why do many commercial aircraft have a red circle on the wing? Many commercial aircraft operated by japanese airlines like JAL and ANA have a red circle on the wing. Look:

Source: Airliners.net
And on this ANA plane, also:

Source: Airliners.net
Why do they have that red circle there?
That would be the Japanese sun symbol which also appears on that nation's flag. You can also see that symbol on the tail of that JAL 777 on top.

Same as the Japanese Flag: