This is television, rather than movies, but: the 1992 Star Trek: The Next Generation episode “The Next Phase” included a a scene in which two characters (Geordi and Ro) who’ve been put ‘out of phase’ in a transporter incident, enter a Romulan ship and discuss the situation in front of a number of Romulans who can neither see nor hear them (due to being ‘in phase’). As Geordi and Ro leave, one of the Romulans–who’d been in plain sight the whole time–gets up and follows them. As it turns out, he is also ‘out of phase’ and so could see and hear them.
Rambo hid in a mud bank.
I think LL Cool J is in plain sight in the couch scene in Toys. I haven’t no found a gif/video of it to check.
Indiana Jones and the Temple of Doom: A man who at first appears to be part of a mural painting turns out to be a real assassin.
The stoned girl on the couch in Lock Stock and Two Smoking Barrels is there the whole time.
There’s a scene in The Godfather in which Michael is sitting and each of Vito’s men shakes his hand, as a sign of allegiance. The guy who ends up being the traitor shakes with his left hand.
The Return of the Pink Panther. The otherwise beautiful Catherine Schell walking around in tbe opening wearing a beard and dressed as a man.
It’s on TV right now. I assume you’re watching.
In a similar vein, Sleuth; Inspector Doppler is on screen for quite a while before it’s revealed that he’s Milo in disguise. I’ve only seen the original, but I didn’t recognize Michael Caine until just before he revealed himself.
Just remembered another one: In Labyrinth, there’s a shot in the middle of a stone corridor, stretching off as far as the eye can see to the left and right. The correct direction to take is Straight forward, into the corridor that’s right there in front of you, and impossible to see
So far, no one’s mentioned Alfred Hitchcock’s cameos in all of his own films? :dubious:
Yep. 
Similarly, the ending of “Indiana Jones and the Last Crusade,” has the transparent bridge leading over to the Grail. So answer me these questions three.
Just the scene I came in here to suggest.
They could always have set it at the White House and made it a political thriller.
Probably not what you mean, but this reminded me of the urban camouflage scene in Be Kind, Rewind.
Nice one. But are Leonard and Sammy literally the same person, or was Sammy a real case that Leonard has imbued with the character of a template for himself? Maybe this has been definitively resolved, but this recent discussion suggests it hasn’t.
You’re thinking of the Lizard People.
Does the Jigsaw in Saw playing dead in the bathroom count?
This is what I first thought of when I read the thread title.
The classic case of this is Edgar Allen Poe’s story The Purloined Letter, the first literary case I know of something literally “hidden in plain sight”. The story has been adapted numerous times on TV (The Wikipedia article lists two, but you can google and find others), but I don’t know of any movie cases
Something of the same sort occurs in Who Framed Roger Rabbit with Acme’s Will, the McGuffin of the film, but Marvin Acme’s using “Disappearing/Reappearing Ink” is a dodge that makes this almost cheating for this case.
In the stalking scene in Memories of Murder, you can see the killer pop up in the background if you know where to look.
One of my favorite “hidden in plain sight” reveal scenes is in the 1964 movie The Long Ships, where Richard Widmark goes to where The Great Bell, “The Mother of Voices” they are seeking is supposed to be, and finds (at first) only a relatively small bell, until his frustrated action shows him the Real bell.
Unfortunately, I can’t find an image or video of the scene. Only the aftermath.