The oak veneer and white pine trend in post '80’s institutional furniture.
Wicker will date a movie.
The Ghetto Blaster dating James Bond:
In the genre of porn, settings will place and date- some Valley or Hollywood producer’s house or rented domicile with Green Shag and a pool like in Boogie Nights. Or nowadays, the shitty Moskobva ghetto apartment with horrible communist wallpaper not unlike a NY ghetto apartment in similarity, ennui, and layout. Wedge rooms with a stove and a pullout.
Military personnel walking around among civilians wearing dress uniforms.
Sympathetic or neutral characters smoking cigarettes, as opposed to only villains or scuzzy, scroungy types.
Filling station attendants. Also big signs advertising gas for 20 cents a gallon.
That has already been mentioned… its redundant.
Funny, though, I have never judged a person by their smoking or lack of smoking habits, same thing with closet drunks, or people who are tattooed or even believe in God and get some comfort from that, or even decide they need to compensate for a little dick or an inferiority complex with guns.
Speaking of Dicks and Guns, the violence factor will often date a movie Pre-Robocop or Post-Robocop.
That would be me. I also don’t have a cell phone. I think I resent the troglodyte label though. I’m posting this from my spiffy new quad-core laptop on my home wireless network whilst watching content I’m streaming from YouTube to my HDTV.
I just hate phones.
Oh, and I date movies by looking for the MCM… in the credits.
I find this notion extremely bizarre. I know of very few people who have a landline that don’t have an answering machine for it. Voicemail is inferior in several ways! You have no way of just glancing at the phone and immediately knowing if there is a message, or how many you have. Many of the phone tree systems are ridiculously slow and annoying to use. And if someone calls, you can’t listen to them leaving the message to decide if you want to pick up. Plus, there is often a monthly fee whereas answering machines are a one time purchase that often add only a small extra price when they are built into cordless stands. I can’t imagine anyone preferring voicemail on a landline. And I would never consider it an example of outdating something else. If anything, the landline itself might eventually become outdated, but not the answering machine attached to it. 
As an aside: dating films by cars only works if they are set in the “modern day,” or whatever year it was filmed was the setting. I doubt you could date, for example, a film set in the 20’s that was made in the 80’s on cars.
What seems to be the most consistent to me is to go by film stock. Some restored and colorized films throw me off though, but otherwise I can usually always get the decade right in a few seconds, including TV shows.
Fashion is a pretty strong one too, especially for science fiction films. Very few science fiction films bother with hairstyles.
Another one that seems to work well for me is breast implants and hair coloring. It’s rather jarring to see larger than a C cup in 70’s and earlier films, and even most 80’s films. Also, it’s pretty rare not to see differently colored hair roots post-1990.
Home and office furnishings are usually a dead giveaway for me. If you see a Nagel, you know it’s not just the eighties, it’s hardcore eighties.
Hell, even the font selection in the titles can give it away.
I’ve stayed in several hotels where you had to do this. I imagine it is so you don’t lose the key and they have to spend money replacing it but I’ve never thought to ask.
One of the things that dates films (and even moreso telly) for me is the film stock. It is easy enough to spot what decade a film came from post-black and white prevalence imho.
A few of these things being mentioned as old fashioned are still regularly done.
Having to walk out onto the runway to board a plane is still done all the time, especially with low cost airlines. Ryanair flying out of Edinburgh Airport, for instance, still makes you do this.
Similarly, leaving keys behind at the reception desk of a hotel is still quite common. I’ve stayed in small hotels/hostels in Florence and Venice which made you do this.
Also, the lift in my apartment block is one of those old fashioned “walk in cupboard” types. There’s an outer door, followed by a “saloon type” inner door, both of which you have to close manually. I’ve also seen a similar lift design in Parisian apartment blocks.
Unplucked eyebrows. On women, anyway.
And I can confirm that the leave-the-key-at-reception rule is still extremely common at smaller European hotels.
Skiing with what appears to be leggings on (for both men and women). I’m not sure if leggings is the right word, but some sort of pants that don’t appear all that warm. Although it wasn’t only in the movies, I know I’ve seen pictures of my grandparents wearing the same thing.
Here’s an example.
Also, really bad green screen work on ski slopes.
I remember my mother once watching the Judy Garland version of “A Star is Born” and saying “that’s how it was in the fifties. Whenever we women went out, we put on white gloves”.
Two things about the 1950s version of “The War of the Worlds”. Seeing the old cars dates the film. But using footage of Northrop’s YB-49 “Flying Wing” when they try to nuke the martians still holds up. You could use that footage in a movie today and it still looks modern.
You could also say looking at movies/tv shows before the late sixties and you almost never see any Black faces.
The one place you would though is at really high end clubs, they would be tending bar or in the band, and usually extremely well liked by the patrons.
Cigarette girls walking around at a club
Cigarettes costing very little. Nickel, Dime, Quarter, some piece of change, less then a dollar.
Smoking on an airplane.
Analogue meters and timers with a moving dial specially when counting down to a deadline.
All that Hi Tec in some Sci Fi but they haven’t gone digital.
ring…ring…“Good morning, General Hospital”.
“This is Jane Doe. Can you tell me what room Joe Blow is in and what his condition is?”
“Certainly…he’s in room 210 on the second floor and his condition is stable. They extracted two bullets from his leg this morning.”
Ha. Try that now. “Joe who? I can’t give that information without the patient’s signed consent.”
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Also: beach parties in movies in the olden days, all the guys wearing Speedo type swimsuits. All the jiggly untoned borderline chubby chicks in sturdy 2-piece swimsuits. With fringe. Lotsa fringe.
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Styles of the decade leaking over into historical/costume pictures. Cleopatra has beestung lips and antenna eyebrows? 30’s. Neferteri has inch long bangs and big red lips? 50’s. Women of ancient Rome have pale lips, yards of Dynel hairpieces, and heavy black eyeliner? 60’s.
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This is pretty obvious, but I always enjoy pointing it out: show a city park or county fair, and all the men are (mostly) wearing hats, long sleeved shirts, and/or suits. Only working men dressed what we think of as casual, and they too would change clothes to something more formal before going out in public. It wasn’t until late 50’s, early 60’s, with Marlon Brando wearing a t-shirt and JFK eschewing the hat, that men started dressing more like we see them today…