Visible crew/equipment: Towards the beginning of the movie when Ralphie's dad is in the basement fixing the furnace and the entire family is staring at the door, you need to keep an eye on the left side of the screen. There is a crewmember in the family room, who is on the screen by mistake. You don't see the person right away, but it is in that sequence when you see the mom in the shot, then you can see the leg of the person very quickly in the background.
Visible crew/equipment: On Christmas morning when Ralphie opens up the bunny suit, you can see stage lights in his glasses.
Visible crew/equipment: In the scene after Ralphie beats up Farcus in which Melinda Dillon finds Randie in the cupboard, you can see a shadow moving continuously on the chair pushed under the table on the right hand side of the shot.
Visible crew/equipment: As the buck teeth are being handed out at the beginning of the classroom scene, the camera pans to follow Miss Shields and you can very briefly see the shadow of the boom microphone on the wall at the top of the screen. (00:15:00)
Visible crew/equipment: During the scene where Ralphie looks out of his window at his snow covered back yard, there is a hat-wearing crew member and some black equipment visible in the lower left of the screen.
Visible crew/equipment: Camera lights (and perhaps some crew, barely) can be seen in Ralphie's sunglasses, when he is imagining himself as a blind person.
Visible crew/equipment: Right when Adult Ralph says "A C+?", Ralph looks from his paper to the blackboard. Near the bottom of his rights glasses lens, you can see a stage light reflected in it, as well as the silhouette of a crew members head. Do not mistake it for the classroom light reflected near the top of the same lens.
Visible crew/equipment: When dad hits the hubcap out of Ralphie's hands, as it spins, you can see the light rigs reflected in it.
Visible crew/equipment: When Ralphie comes into the kitchen, he passes in front of the camera. As he does so, you can see the shadow of the camera on him.
Visible crew/equipment: As Santa's foot closes in on Ralphie's face to push him down the slide, the shadow on his boot is the squared light shade of the camera.
Visible crew/equipment: During the parade, the camera moves in and back a couple of times and the operator's shadow is visible left screen. This is really obvious after the Wizard of Oz characters walk by.
Visible crew/equipment: When the mom is sitting on the floor holding the broken lamp, as the dad runs in, you can see the shadow of a boom mic near the mom's left shoulder.
Answer: It's most likely a reference to the twin-bed movie standards from the time in which the movie takes place (late '30s to early '40s).