In a deleted scene at the very end of Back to the Future we find Marty’s father, George, in 1985, at his desk looking through a digital scrapbook created by Dr. Emmett Brown. He plugs it in and stops at a page showing a 1955 newspaper clipping with the headline, “Police Quell Near Riot At School Dance.” It shows a photograph of Marty on stage, rocking out to Chuck Berry’s "Johnny B. Goode" and, originally, Bill Haley’s "Rock Around The Clock."
The image stirs something in George; it feels oddly familiar. He gives it a long look and shakes his head. He murmurs, “Nah. Couldn’t be.” He pauses briefly as the camera pans closer toward the photo. Then he whispers, “But it is.”
This scene was cut from the first three drafts. Instead, writer Bob Gale and director Robert Zemeckis settled for an ending where Biff is the one that becomes mildly self-aware of Marty’s time traveling, rather than George.
Nearly four decades after the first Back to the Future, fans are still unconvinced that neither of Marty McFly’s parents were able to pick up on his time traveling — not even after “Calvin Klein’s” little vanishing act in 1955 and the birth of their son Martin years later. It just seemed too surreal to be true.
And why wouldn’t it be? 1955 Marty “Klein” used a skateboard before it was even invented, made three references (Darth Vader, Planet Vulcan, and the Vulcan hand salute) to two popular sci-fi franchises (Star Wars and Star Trek) before they were created, wore a radiation suit years before most people knew what it was, and even performed a song years before it was released in public. He “predicted” cafe janitor Goldie Wilson’s political rise to power decades before he became mayor and wore a brand of underwear that did not exist in retail until years later.
While performing Johnny B. Goode at the Enchantment Under The Sea dance, Marty executed tricks that would only become famous after 1955, like Angus Young’s infamous floor spin or the way Jimi Hendrix would play his guitar behind his head.
On a more personal level, Marty called his father “dad” too many times for it to be construed as just an accident or a weird nickname. He even told his parents back in 1955 about a specific event in their future son’s life that presumably happened as warned, and if that wasn’t enough to get them suspecting about who “Calvin” really was, I don't know what is.
Marty’s father is far from gullible however, even in his youth. Given what we know of George and his avid sci-fi obsession (and the hints Marty’s dropped here and there), it’s not too unlikely to assume that George was able to put the pieces together and figure out the truth: that the Marty of his past is the same Marty of his present. If he knows, it’s not too far off to assume that Lorraine knows too.
Officially Not Canon?
The inclusion of the “hydraulic scrapbook” and George’s scene with the newspaper clipping in the first draft ended years of debate and fan speculation theorizing what George knew or didn’t know, about Marty and “Calvin Klein.” He knew.
Unfortunately, George’s purported awareness of Marty’s time traveling has never been officially confirmed by either Zemeckis or Gale in any interview following the release of the #BackToTheFuture movies. Maybe there’s no need to confirm; after all, we have the draft, and the draft basically speaks for itself.
It’s best to treat this the same way we would any deleted scene: It happened, they just didn’t show it. After all, just because something wasn’t shown onscreen, doesn’t mean it didn’t happen off-screen. The way George behaved after Marty returned from 1955 to the revised 1985 is way too telling of what he probably already knew about “Calvin” and his son. Repeating the same advice he was given, putting Marty’s radiation suit on the front cover of his novel — if there’s one thing we all learned from Back to the Future, it’s that nothing is ever a coincidence.