Invasion of Japan, invasion stripes on a/c?

I don't know the answer to your question but I'm wondering if they would have been needed. I would think that, by that stage of the war, just about any aircraft in the air would have been US or allied. ;~)

Was it not nearly the same in the ETO by D-Day?

Well, having done my MA thesis on the Invasion plans, there would've been some

10,000 Japanese aircraft in the air from X-3 (when they expected to discover the assault shipping en route to Kyushu) to X+5 (when the JNAF and JAAF expected to have expended those aircraft). Half were suicide aircraft, and half were conventional attack, recon, and fighter aircraft. Whether or not the conventional aircraft would've been expended as kamikazes is still an unanswered question. As is how many of those aircraft would have been knocked out on the ground by Allied (USAAF, USN, USMC, and Royal Navy) air attack.

10,000 Japanese aircraft in the air from X-3 (when they expected to discover the assault shipping en route to Kyushu) to X+5 (when the JNAF and JAAF expected to have expended those aircraft). Half were suicide aircraft, and half were conventional attack, recon, and fighter aircraft. Whether or not the conventional aircraft would've been expended as kamikazes is still an unanswered question. As is how many of those aircraft would have been knocked out on the ground by Allied (USAAF, USN, USMC, and Royal Navy) air attack.

Matt, having researched the topic, can you answer the OP's question? Would there have been recognition markings on the Allied aircraft, and what would they have looked like?

Fifth Air Force already had a roughly uniform system of bands. Navy might have added white bands on their dark blue planes.