The US insignia was changed several times during WWI, and each time was to make it easier to distinguish from the enemy.
At the start of the war we had the 6-position blue roundel with white star and red circle in the center. Our own guys in the heat of battle kept mistaking the red dot or a Japanese meatball and shooting at our own planes. So they dropped the red dot, but the big round 6-position insignia could still be mistaken for a meatball, and the friendly fire incidents continued.
So in the summer of 43 we added the two white bars with the red outline around the whole thing, completely changing the shape of the emblem, an removed it from two positions so it was only on the top and bottom of the wing once. This worked to an extent, but our guys still saw all that red and didn't wait for positive ID to shoot!
So finally the red border was turned to the same blue as the circle (which is why the white bars appear to go
into the circle) in Sept 43, leaving red off entirely. That finally worked!
Red was not returned to the emblem until 1947, when the red center stripes were added to the bars, and we still stay with the 4-position arrangement.