Strange subliminal message appears on History Channel show “Unidentified” about UFOS

Well my friend and I had noticed a flash on the screen of the latest episode called S1 E5 titled: “The Atomic Connection”. After a clip was played of a nuclear bomb going off while watching the show my eye had caught this written image so I blurted out.

“Were those words that displayed on the screen? I think it was a subliminal message.”

My friend remarked, “I think you’re right let’s look because that was weird.”

So my friend rewinds the show, and it took a few tries because the image had appeared so quickly to capture it when it came up, finally we were able to pause it right on the frame. The result below. I took a picture with my phone.

The words say, “GREEN SEPARATION” and it is upside down.

Why was it upside down?
What does “Green Separation” mean?
Why would the show use this as a subliminal message?

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